diff --git a/src/CultureInfoGenerator/Program.cs b/src/CultureInfoGenerator/Program.cs
index 76882d3ce0..1e1da87b91 100644
--- a/src/CultureInfoGenerator/Program.cs
+++ b/src/CultureInfoGenerator/Program.cs
@@ -5,7 +5,8 @@ using System;
 using System.Globalization;
 using System.IO;
 using System.Linq;
-using Microsoft.Dnx.Runtime;using Microsoft.Win32;
+using Microsoft.Dnx.Runtime;
+using Microsoft.Win32;
 
 namespace CultureInfoGenerator
 {
diff --git a/src/Microsoft.AspNet.Localization/AcceptLanguageHeaderRequestCultureProvider.cs b/src/Microsoft.AspNet.Localization/AcceptLanguageHeaderRequestCultureProvider.cs
index 1368efb4ed..adf41adc9a 100644
--- a/src/Microsoft.AspNet.Localization/AcceptLanguageHeaderRequestCultureProvider.cs
+++ b/src/Microsoft.AspNet.Localization/AcceptLanguageHeaderRequestCultureProvider.cs
@@ -1,11 +1,11 @@
 // Copyright (c) .NET Foundation. All rights reserved. 
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information. 
 
+using System;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Http;
 using Microsoft.Extensions.Globalization;
-using Microsoft.Extensions.Internal;
 using Microsoft.Net.Http.Headers;
 
 namespace Microsoft.AspNet.Localization
@@ -23,8 +23,13 @@ namespace Microsoft.AspNet.Localization
         public int MaximumAcceptLanguageHeaderValuesToTry { get; set; } = 3;
 
         /// <inheritdoc />
-        public override Task<RequestCulture> DetermineRequestCulture([NotNull] HttpContext httpContext)
+        public override Task<RequestCulture> DetermineRequestCulture(HttpContext httpContext)
         {
+            if (httpContext == null)
+            {
+                throw new ArgumentNullException(nameof(httpContext));
+            }
+
             var acceptLanguageHeader = httpContext.Request.GetTypedHeaders().AcceptLanguage;
 
             if (acceptLanguageHeader == null || acceptLanguageHeader.Count == 0)
@@ -40,7 +45,7 @@ namespace Microsoft.AspNet.Localization
                 // attempt to parse as a CultureInfo to mitigate potentially spinning CPU on lots of parse attempts.
                 languages = languages.Take(MaximumAcceptLanguageHeaderValuesToTry);
             }
-            
+
             var orderedLanguages = languages.OrderByDescending(h => h, StringWithQualityHeaderValueComparer.QualityComparer)
                 .ToList();
 
diff --git a/src/Microsoft.AspNet.Localization/ApplicationBuilderExtensions.cs b/src/Microsoft.AspNet.Localization/ApplicationBuilderExtensions.cs
index 37080d6dc2..6d49afbb66 100644
--- a/src/Microsoft.AspNet.Localization/ApplicationBuilderExtensions.cs
+++ b/src/Microsoft.AspNet.Localization/ApplicationBuilderExtensions.cs
@@ -1,8 +1,8 @@
 // Copyright (c) .NET Foundation. All rights reserved. 
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information. 
 
+using System;
 using Microsoft.AspNet.Localization;
-using Microsoft.Extensions.Internal;
 
 namespace Microsoft.AspNet.Builder
 {
@@ -17,8 +17,13 @@ namespace Microsoft.AspNet.Builder
         /// </summary>
         /// <param name="builder">The <see cref="IApplicationBuilder"/>.</param>
         /// <returns>The <see cref="IApplicationBuilder"/>.</returns>
-        public static IApplicationBuilder UseRequestLocalization([NotNull] this IApplicationBuilder builder)
+        public static IApplicationBuilder UseRequestLocalization(this IApplicationBuilder builder)
         {
+            if (builder == null)
+            {
+                throw new ArgumentNullException(nameof(builder));
+            }
+
             var options = new RequestLocalizationOptions();
 
             return UseRequestLocalization(builder, options);
@@ -32,8 +37,20 @@ namespace Microsoft.AspNet.Builder
         /// <param name="options">The options to configure the middleware with.</param>
         /// <returns>The <see cref="IApplicationBuilder"/>.</returns>
         public static IApplicationBuilder UseRequestLocalization(
-            [NotNull] this IApplicationBuilder builder,
-            [NotNull] RequestLocalizationOptions options)
-            => builder.UseMiddleware<RequestLocalizationMiddleware>(options);
+            this IApplicationBuilder builder,
+            RequestLocalizationOptions options)
+        {
+            if (builder == null)
+            {
+                throw new ArgumentNullException(nameof(builder));
+            }
+
+            if (options == null)
+            {
+                throw new ArgumentNullException(nameof(options));
+            }
+
+            return builder.UseMiddleware<RequestLocalizationMiddleware>(options);
+        }
     }
 }
\ No newline at end of file
diff --git a/src/Microsoft.AspNet.Localization/CookieRequestCultureProvider.cs b/src/Microsoft.AspNet.Localization/CookieRequestCultureProvider.cs
index 305f0796db..22c98c1e15 100644
--- a/src/Microsoft.AspNet.Localization/CookieRequestCultureProvider.cs
+++ b/src/Microsoft.AspNet.Localization/CookieRequestCultureProvider.cs
@@ -5,7 +5,6 @@ using System;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Http;
 using Microsoft.Extensions.Globalization;
-using Microsoft.Extensions.Internal;
 
 namespace Microsoft.AspNet.Localization
 {
@@ -17,7 +16,7 @@ namespace Microsoft.AspNet.Localization
         private static readonly char[] _cookieSeparator = new[] { '|' };
         private static readonly string _culturePrefix = "c=";
         private static readonly string _uiCulturePrefix = "uic=";
-        
+
         /// <summary>
         /// Represent the default cookie name used to track the user's preferred culture information, which is "ASPNET_CULTURE".
         /// </summary>
@@ -30,8 +29,13 @@ namespace Microsoft.AspNet.Localization
         public string CookieName { get; set; } = DefaultCookieName;
 
         /// <inheritdoc />
-        public override Task<RequestCulture> DetermineRequestCulture([NotNull] HttpContext httpContext)
+        public override Task<RequestCulture> DetermineRequestCulture(HttpContext httpContext)
         {
+            if (httpContext == null)
+            {
+                throw new ArgumentNullException(nameof(httpContext));
+            }
+
             var cookie = httpContext.Request.Cookies[CookieName];
 
             if (cookie == null)
@@ -51,8 +55,13 @@ namespace Microsoft.AspNet.Localization
         /// </summary>
         /// <param name="requestCulture">The <see cref="RequestCulture"/>.</param>
         /// <returns>The cookie value.</returns>
-        public static string MakeCookieValue([NotNull] RequestCulture requestCulture)
+        public static string MakeCookieValue(RequestCulture requestCulture)
         {
+            if (requestCulture == null)
+            {
+                throw new ArgumentNullException(nameof(requestCulture));
+            }
+
             var seperator = _cookieSeparator[0].ToString();
 
             return string.Join(seperator,
@@ -66,7 +75,7 @@ namespace Microsoft.AspNet.Localization
         /// </summary>
         /// <param name="value">The cookie value to parse.</param>
         /// <returns>The <see cref="RequestCulture"/> or <c>null</c> if parsing fails.</returns>
-        public static RequestCulture ParseCookieValue([NotNull] string value)
+        public static RequestCulture ParseCookieValue(string value)
         {
             if (string.IsNullOrWhiteSpace(value))
             {
diff --git a/src/Microsoft.AspNet.Localization/CustomRequestCultureProvider.cs b/src/Microsoft.AspNet.Localization/CustomRequestCultureProvider.cs
index 112123b847..4af0faabda 100644
--- a/src/Microsoft.AspNet.Localization/CustomRequestCultureProvider.cs
+++ b/src/Microsoft.AspNet.Localization/CustomRequestCultureProvider.cs
@@ -4,7 +4,6 @@
 using System;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Http;
-using Microsoft.Extensions.Internal;
 
 namespace Microsoft.AspNet.Localization
 {
@@ -19,13 +18,25 @@ namespace Microsoft.AspNet.Localization
         /// Creates a new <see cref="CustomRequestCultureProvider"/> using the specified delegate.
         /// </summary>
         /// <param name="provider">The provider delegate.</param>
-        public CustomRequestCultureProvider([NotNull] Func<HttpContext, Task<RequestCulture>> provider)
+        public CustomRequestCultureProvider(Func<HttpContext, Task<RequestCulture>> provider)
         {
+            if (provider == null)
+            {
+                throw new ArgumentNullException(nameof(provider));
+            }
+
             _provider = provider;
         }
 
         /// <inheritdoc />
-        public override Task<RequestCulture> DetermineRequestCulture([NotNull] HttpContext httpContext)
-            => _provider(httpContext);
+        public override Task<RequestCulture> DetermineRequestCulture(HttpContext httpContext)
+        {
+            if (httpContext == null)
+            {
+                throw new ArgumentNullException(nameof(httpContext));
+            }
+
+            return _provider(httpContext);
+        }
     }
 }
diff --git a/src/Microsoft.AspNet.Localization/QueryStringRequestCultureProvider.cs b/src/Microsoft.AspNet.Localization/QueryStringRequestCultureProvider.cs
index bdf6dc6c1f..ea1398ed9f 100644
--- a/src/Microsoft.AspNet.Localization/QueryStringRequestCultureProvider.cs
+++ b/src/Microsoft.AspNet.Localization/QueryStringRequestCultureProvider.cs
@@ -1,10 +1,10 @@
 // Copyright (c) .NET Foundation. All rights reserved. 
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information. 
 
+using System;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Http;
 using Microsoft.Extensions.Globalization;
-using Microsoft.Extensions.Internal;
 
 namespace Microsoft.AspNet.Localization
 {
@@ -27,8 +27,13 @@ namespace Microsoft.AspNet.Localization
         public string UIQueryStringKey { get; set; } = "ui-culture";
 
         /// <inheritdoc />
-        public override Task<RequestCulture> DetermineRequestCulture([NotNull] HttpContext httpContext)
+        public override Task<RequestCulture> DetermineRequestCulture(HttpContext httpContext)
         {
+            if (httpContext == null)
+            {
+                throw new ArgumentNullException(nameof(httpContext));
+            }
+
             var request = httpContext.Request;
             if (!request.QueryString.HasValue)
             {
@@ -65,7 +70,7 @@ namespace Microsoft.AspNet.Localization
                 // Value for UI culture but not for culture so default to UI culture value for both
                 queryCulture = queryUICulture;
             }
-            
+
             var culture = CultureInfoCache.GetCultureInfo(queryCulture);
             var uiCulture = CultureInfoCache.GetCultureInfo(queryUICulture);
 
diff --git a/src/Microsoft.AspNet.Localization/RequestCulture.cs b/src/Microsoft.AspNet.Localization/RequestCulture.cs
index 31cf028760..175a05ec0b 100644
--- a/src/Microsoft.AspNet.Localization/RequestCulture.cs
+++ b/src/Microsoft.AspNet.Localization/RequestCulture.cs
@@ -1,8 +1,8 @@
 // Copyright (c) .NET Foundation. All rights reserved. 
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information. 
 
+using System;
 using System.Globalization;
-using Microsoft.Extensions.Internal;
 
 namespace Microsoft.AspNet.Localization
 {
@@ -16,10 +16,9 @@ namespace Microsoft.AspNet.Localization
         /// properties set to the same <see cref="CultureInfo"/> value.
         /// </summary>
         /// <param name="culture">The <see cref="CultureInfo"/> for the request.</param>
-        public RequestCulture([NotNull] CultureInfo culture)
-            : this (culture, culture)
+        public RequestCulture(CultureInfo culture)
+            : this(culture, culture)
         {
-
         }
 
         /// <summary>
@@ -28,8 +27,18 @@ namespace Microsoft.AspNet.Localization
         /// </summary>
         /// <param name="culture">The <see cref="CultureInfo"/> for the request to be used for formatting.</param>
         /// <param name="uiCulture">The <see cref="CultureInfo"/> for the request to be used for text, i.e. language.</param>
-        public RequestCulture([NotNull] CultureInfo culture, [NotNull] CultureInfo uiCulture)
+        public RequestCulture(CultureInfo culture, CultureInfo uiCulture)
         {
+            if (culture == null)
+            {
+                throw new ArgumentNullException(nameof(culture));
+            }
+
+            if (uiCulture == null)
+            {
+                throw new ArgumentNullException(nameof(uiCulture));
+            }
+
             Culture = culture;
             UICulture = uiCulture;
         }
diff --git a/src/Microsoft.AspNet.Localization/RequestCultureFeature.cs b/src/Microsoft.AspNet.Localization/RequestCultureFeature.cs
index 0b952984fb..1fb00c9895 100644
--- a/src/Microsoft.AspNet.Localization/RequestCultureFeature.cs
+++ b/src/Microsoft.AspNet.Localization/RequestCultureFeature.cs
@@ -1,7 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved. 
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information. 
 
-using Microsoft.Extensions.Internal;
+using System;
 
 namespace Microsoft.AspNet.Localization
 {
@@ -15,8 +15,13 @@ namespace Microsoft.AspNet.Localization
         /// </summary>
         /// <param name="requestCulture">The <see cref="Localization.RequestCulture"/>.</param>
         /// <param name="provider">The <see cref="IRequestCultureProvider"/>.</param>
-        public RequestCultureFeature([NotNull] RequestCulture requestCulture, IRequestCultureProvider provider)
+        public RequestCultureFeature(RequestCulture requestCulture, IRequestCultureProvider provider)
         {
+            if (requestCulture == null)
+            {
+                throw new ArgumentNullException(nameof(requestCulture));
+            }
+
             RequestCulture = requestCulture;
             Provider = provider;
         }
diff --git a/src/Microsoft.AspNet.Localization/RequestLocalizationMiddleware.cs b/src/Microsoft.AspNet.Localization/RequestLocalizationMiddleware.cs
index a5df668ca5..825e7c4f8c 100644
--- a/src/Microsoft.AspNet.Localization/RequestLocalizationMiddleware.cs
+++ b/src/Microsoft.AspNet.Localization/RequestLocalizationMiddleware.cs
@@ -1,13 +1,13 @@
 // Copyright (c) .NET Foundation. All rights reserved. 
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information. 
 
+using System;
 using System.Globalization;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Builder;
 using Microsoft.AspNet.Http;
 using Microsoft.AspNet.Http.Features;
-using Microsoft.Extensions.Internal;
 
 namespace Microsoft.AspNet.Localization
 {
@@ -19,14 +19,24 @@ namespace Microsoft.AspNet.Localization
     {
         private readonly RequestDelegate _next;
         private readonly RequestLocalizationOptions _options;
-        
+
         /// <summary>
         /// Creates a new <see cref="RequestLocalizationMiddleware"/>.
         /// </summary>
         /// <param name="next">The <see cref="RequestDelegate"/> representing the next middleware in the pipeline.</param>
         /// <param name="options">The <see cref="RequestLocalizationOptions"/> representing the options for the <see cref="RequestLocalizationMiddleware"/>.</param>
-        public RequestLocalizationMiddleware([NotNull] RequestDelegate next, [NotNull] RequestLocalizationOptions options)
+        public RequestLocalizationMiddleware(RequestDelegate next, RequestLocalizationOptions options)
         {
+            if (next == null)
+            {
+                throw new ArgumentNullException(nameof(next));
+            }
+
+            if (options == null)
+            {
+                throw new ArgumentNullException(nameof(options));
+            }
+
             _next = next;
             _options = options;
         }
@@ -36,8 +46,13 @@ namespace Microsoft.AspNet.Localization
         /// </summary>
         /// <param name="context">The <see cref="HttpContext"/>.</param>
         /// <returns>A <see cref="Task"/> that completes when the middleware has completed processing.</returns>
-        public async Task Invoke([NotNull] HttpContext context)
+        public async Task Invoke(HttpContext context)
         {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
             var requestCulture = _options.DefaultRequestCulture ??
                 new RequestCulture(CultureInfo.CurrentCulture, CultureInfo.CurrentUICulture);
 
diff --git a/src/Microsoft.AspNet.Localization/project.json b/src/Microsoft.AspNet.Localization/project.json
index 6b2f05db67..450bf4c204 100644
--- a/src/Microsoft.AspNet.Localization/project.json
+++ b/src/Microsoft.AspNet.Localization/project.json
@@ -5,14 +5,13 @@
         "type": "git",
         "url": "https://github.com/aspnet/localization"
     },
+    "compilationOptions": {
+        "warningsAsErrors": true
+    },
     "dependencies": {
         "Microsoft.AspNet.Http.Extensions": "1.0.0-*",
         "Microsoft.Extensions.Globalization.CultureInfoCache": "1.0.0-*",
-        "Microsoft.Extensions.Localization.Abstractions": "1.0.0-*",
-        "Microsoft.Extensions.NotNullAttribute.Sources": {
-            "type": "build",
-            "version": "1.0.0-*"
-        }
+        "Microsoft.Extensions.Localization.Abstractions": "1.0.0-*"
     },
     "frameworks": {
         "dnx451": { },
diff --git a/src/Microsoft.Extensions.Globalization.CultureInfoCache/project.json b/src/Microsoft.Extensions.Globalization.CultureInfoCache/project.json
index 8bb390e713..bcab9ffe4d 100644
--- a/src/Microsoft.Extensions.Globalization.CultureInfoCache/project.json
+++ b/src/Microsoft.Extensions.Globalization.CultureInfoCache/project.json
@@ -5,7 +5,8 @@
         "type": "git",
         "url": "https://github.com/aspnet/localization"
     },
-    "dependencies": {
+    "compilationOptions": {
+        "warningsAsErrors": true
     },
     "frameworks": {
         "dnx451": { },
diff --git a/src/Microsoft.Extensions.Localization.Abstractions/LocalizedString.cs b/src/Microsoft.Extensions.Localization.Abstractions/LocalizedString.cs
index a8db327609..378d5edb21 100644
--- a/src/Microsoft.Extensions.Localization.Abstractions/LocalizedString.cs
+++ b/src/Microsoft.Extensions.Localization.Abstractions/LocalizedString.cs
@@ -1,7 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved. 
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information. 
 
-using Microsoft.Extensions.Internal;
+using System;
 
 namespace Microsoft.Extensions.Localization
 {
@@ -15,10 +15,9 @@ namespace Microsoft.Extensions.Localization
         /// </summary>
         /// <param name="name">The name of the string in the resource it was loaded from.</param>
         /// <param name="value">The actual string.</param>
-        public LocalizedString([NotNull] string name, [NotNull] string value)
+        public LocalizedString(string name, string value)
             : this(name, value, resourceNotFound: false)
         {
-
         }
 
         /// <summary>
@@ -27,14 +26,24 @@ namespace Microsoft.Extensions.Localization
         /// <param name="name">The name of the string in the resource it was loaded from.</param>
         /// <param name="value">The actual string.</param>
         /// <param name="resourceNotFound">Whether the string was found in a resource. Set this to <c>false</c> to indicate an alternate string value was used.</param>
-        public LocalizedString([NotNull] string name, [NotNull] string value, bool resourceNotFound)
+        public LocalizedString(string name, string value, bool resourceNotFound)
         {
+            if (name == null)
+            {
+                throw new ArgumentNullException(nameof(name));
+            }
+
+            if (value == null)
+            {
+                throw new ArgumentNullException(nameof(value));
+            }
+
             Name = name;
             Value = value;
             ResourceNotFound = resourceNotFound;
         }
 
-        public static implicit operator string (LocalizedString localizedString)
+        public static implicit operator string(LocalizedString localizedString)
         {
             return localizedString.Value;
         }
diff --git a/src/Microsoft.Extensions.Localization.Abstractions/StringLocalizerExtensions.cs b/src/Microsoft.Extensions.Localization.Abstractions/StringLocalizerExtensions.cs
index ff48da00e1..73d254bab9 100644
--- a/src/Microsoft.Extensions.Localization.Abstractions/StringLocalizerExtensions.cs
+++ b/src/Microsoft.Extensions.Localization.Abstractions/StringLocalizerExtensions.cs
@@ -1,8 +1,8 @@
 // Copyright (c) .NET Foundation. All rights reserved. 
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information. 
 
+using System;
 using System.Collections.Generic;
-using Microsoft.Extensions.Internal;
 
 namespace Microsoft.Extensions.Localization
 {
@@ -15,8 +15,21 @@ namespace Microsoft.Extensions.Localization
         /// <param name="name">The name of the string resource.</param>
         /// <returns>The string resource as a <see cref="LocalizedString"/>.</returns>
         public static LocalizedString GetString(
-            [NotNull] this IStringLocalizer stringLocalizer,
-            [NotNull] string name) => stringLocalizer[name];
+            this IStringLocalizer stringLocalizer,
+            string name)
+        {
+            if (stringLocalizer == null)
+            {
+                throw new ArgumentNullException(nameof(stringLocalizer));
+            }
+
+            if (name == null)
+            {
+                throw new ArgumentNullException(nameof(name));
+            }
+
+            return stringLocalizer[name];
+        }
 
         /// <summary>
         /// Gets the string resource with the given name and formatted with the supplied arguments.
@@ -26,16 +39,36 @@ namespace Microsoft.Extensions.Localization
         /// <param name="arguments">The values to format the string with.</param>
         /// <returns>The formatted string resource as a <see cref="LocalizedString"/>.</returns>
         public static LocalizedString GetString(
-            [NotNull] this IStringLocalizer stringLocalizer,
-            [NotNull] string name,
-            params object[] arguments) => stringLocalizer[name, arguments];
+            this IStringLocalizer stringLocalizer,
+            string name,
+            params object[] arguments)
+        {
+            if (stringLocalizer == null)
+            {
+                throw new ArgumentNullException(nameof(stringLocalizer));
+            }
+
+            if (name == null)
+            {
+                throw new ArgumentNullException(nameof(name));
+            }
+
+            return stringLocalizer[name, arguments];
+        }
 
         /// <summary>
         /// Gets all string resources including those for ancestor cultures.
         /// </summary>
         /// <param name="stringLocalizer">The <see cref="IStringLocalizer"/>.</param>
         /// <returns>The string resources.</returns>
-        public static IEnumerable<LocalizedString> GetAllStrings([NotNull] this IStringLocalizer stringLocalizer) =>
-            stringLocalizer.GetAllStrings(includeAncestorCultures: true);
+        public static IEnumerable<LocalizedString> GetAllStrings(this IStringLocalizer stringLocalizer)
+        {
+            if (stringLocalizer == null)
+            {
+                throw new ArgumentNullException(nameof(stringLocalizer));
+            }
+
+            return stringLocalizer.GetAllStrings(includeAncestorCultures: true);
+        }
     }
 }
diff --git a/src/Microsoft.Extensions.Localization.Abstractions/StringLocalizerOfT.cs b/src/Microsoft.Extensions.Localization.Abstractions/StringLocalizerOfT.cs
index 2c19e7fbaa..7007122b67 100644
--- a/src/Microsoft.Extensions.Localization.Abstractions/StringLocalizerOfT.cs
+++ b/src/Microsoft.Extensions.Localization.Abstractions/StringLocalizerOfT.cs
@@ -1,9 +1,9 @@
 // Copyright (c) .NET Foundation. All rights reserved. 
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information. 
 
+using System;
 using System.Collections.Generic;
 using System.Globalization;
-using Microsoft.Extensions.Internal;
 
 namespace Microsoft.Extensions.Localization
 {
@@ -19,8 +19,13 @@ namespace Microsoft.Extensions.Localization
         /// Creates a new <see cref="StringLocalizer{TResourceSource}"/>.
         /// </summary>
         /// <param name="factory">The <see cref="IStringLocalizerFactory"/> to use.</param>
-        public StringLocalizer([NotNull] IStringLocalizerFactory factory)
+        public StringLocalizer(IStringLocalizerFactory factory)
         {
+            if (factory == null)
+            {
+                throw new ArgumentNullException(nameof(factory));
+            }
+
             _localizer = factory.Create(typeof(TResourceSource));
         }
 
@@ -28,11 +33,32 @@ namespace Microsoft.Extensions.Localization
         public virtual IStringLocalizer WithCulture(CultureInfo culture) => _localizer.WithCulture(culture);
 
         /// <inheritdoc />
-        public virtual LocalizedString this[[NotNull] string name] => _localizer[name];
+        public virtual LocalizedString this[string name]
+        {
+            get
+            {
+                if (name == null)
+                {
+                    throw new ArgumentNullException(nameof(name));
+                }
+
+                return _localizer[name];
+            }
+        }
 
         /// <inheritdoc />
-        public virtual LocalizedString this[[NotNull] string name, params object[] arguments] =>
-            _localizer[name, arguments];
+        public virtual LocalizedString this[string name, params object[] arguments]
+        {
+            get
+            {
+                if (name == null)
+                {
+                    throw new ArgumentNullException(nameof(name));
+                }
+
+                return _localizer[name, arguments];
+            }
+        }
 
         /// <inheritdoc />
         public IEnumerable<LocalizedString> GetAllStrings(bool includeAncestorCultures) =>
diff --git a/src/Microsoft.Extensions.Localization.Abstractions/project.json b/src/Microsoft.Extensions.Localization.Abstractions/project.json
index 323c5af77e..7a35dfaf2e 100644
--- a/src/Microsoft.Extensions.Localization.Abstractions/project.json
+++ b/src/Microsoft.Extensions.Localization.Abstractions/project.json
@@ -5,11 +5,8 @@
         "type": "git",
         "url": "https://github.com/aspnet/localization"
     },
-    "dependencies": {
-        "Microsoft.Extensions.NotNullAttribute.Sources": {
-            "type": "build",
-            "version": "1.0.0-*"
-        }
+    "compilationOptions": {
+        "warningsAsErrors": true
     },
     "frameworks": {
         "dnx451": { },
diff --git a/src/Microsoft.Extensions.Localization/Internal/AssemblyWrapper.cs b/src/Microsoft.Extensions.Localization/Internal/AssemblyWrapper.cs
index be32e83867..b0c3c2bce1 100644
--- a/src/Microsoft.Extensions.Localization/Internal/AssemblyWrapper.cs
+++ b/src/Microsoft.Extensions.Localization/Internal/AssemblyWrapper.cs
@@ -1,16 +1,21 @@
 // Copyright (c) .NET Foundation. All rights reserved. 
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using System.IO;
 using System.Reflection;
-using Microsoft.Extensions.Internal;
 
 namespace Microsoft.Extensions.Localization.Internal
 {
     public class AssemblyWrapper
     {
-        public AssemblyWrapper([NotNull] Assembly assembly)
+        public AssemblyWrapper(Assembly assembly)
         {
+            if (assembly == null)
+            {
+                throw new ArgumentNullException(nameof(assembly));
+            }
+
             Assembly = assembly;
         }
 
diff --git a/src/Microsoft.Extensions.Localization/LocalizationServiceCollectionExtensions.cs b/src/Microsoft.Extensions.Localization/LocalizationServiceCollectionExtensions.cs
index f09d4ec5d3..25e619293d 100644
--- a/src/Microsoft.Extensions.Localization/LocalizationServiceCollectionExtensions.cs
+++ b/src/Microsoft.Extensions.Localization/LocalizationServiceCollectionExtensions.cs
@@ -3,7 +3,6 @@
 
 using System;
 using Microsoft.Extensions.DependencyInjection.Extensions;
-using Microsoft.Extensions.Internal;
 using Microsoft.Extensions.Localization;
 
 namespace Microsoft.Extensions.DependencyInjection
@@ -18,8 +17,13 @@ namespace Microsoft.Extensions.DependencyInjection
         /// </summary>
         /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
         /// <returns>The <see cref="IServiceCollection"/>.</returns>
-        public static IServiceCollection AddLocalization([NotNull] this IServiceCollection services)
+        public static IServiceCollection AddLocalization(this IServiceCollection services)
         {
+            if (services == null)
+            {
+                throw new ArgumentNullException(nameof(services));
+            }
+
             return AddLocalization(services, setupAction: null);
         }
 
@@ -30,9 +34,14 @@ namespace Microsoft.Extensions.DependencyInjection
         /// <param name="setupAction">An action to configure the <see cref="LocalizationOptions"/>.</param>
         /// <returns>The <see cref="IServiceCollection"/>.</returns>
         public static IServiceCollection AddLocalization(
-            [NotNull] this IServiceCollection services,
+            this IServiceCollection services,
             Action<LocalizationOptions> setupAction)
         {
+            if (services == null)
+            {
+                throw new ArgumentNullException(nameof(services));
+            }
+
             services.TryAdd(new ServiceDescriptor(
                 typeof(IStringLocalizerFactory),
                 typeof(ResourceManagerStringLocalizerFactory),
diff --git a/src/Microsoft.Extensions.Localization/ResourceManagerStringLocalizer.cs b/src/Microsoft.Extensions.Localization/ResourceManagerStringLocalizer.cs
index a7d6101c23..46139de4c0 100644
--- a/src/Microsoft.Extensions.Localization/ResourceManagerStringLocalizer.cs
+++ b/src/Microsoft.Extensions.Localization/ResourceManagerStringLocalizer.cs
@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved. 
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information. 
 
+using System;
 using System.Collections;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
@@ -34,24 +35,47 @@ namespace Microsoft.Extensions.Localization
         /// <param name="baseName">The base name of the embedded resource in the <see cref="Assembly"/> that contains the strings.</param>
         /// <param name="resourceNamesCache">Cache of the list of strings for a given resource assembly name.</param>
         public ResourceManagerStringLocalizer(
-            [NotNull] ResourceManager resourceManager,
-            [NotNull] Assembly resourceAssembly,
-            [NotNull] string baseName,
-            [NotNull] IResourceNamesCache resourceNamesCache)
+            ResourceManager resourceManager,
+            Assembly resourceAssembly,
+            string baseName,
+            IResourceNamesCache resourceNamesCache)
             : this(resourceManager, new AssemblyWrapper(resourceAssembly), baseName, resourceNamesCache)
         {
-            
+            if (resourceAssembly == null)
+            {
+                throw new ArgumentNullException(nameof(resourceAssembly));
+            }
         }
 
         /// <summary>
         /// Intended for testing purposes only.
         /// </summary>
         public ResourceManagerStringLocalizer(
-            [NotNull] ResourceManager resourceManager,
-            [NotNull] AssemblyWrapper resourceAssemblyWrapper,
-            [NotNull] string baseName,
-            [NotNull] IResourceNamesCache resourceNamesCache)
+            ResourceManager resourceManager,
+            AssemblyWrapper resourceAssemblyWrapper,
+            string baseName,
+            IResourceNamesCache resourceNamesCache)
         {
+            if (resourceManager == null)
+            {
+                throw new ArgumentNullException(nameof(resourceManager));
+            }
+
+            if (resourceAssemblyWrapper == null)
+            {
+                throw new ArgumentNullException(nameof(resourceAssemblyWrapper));
+            }
+
+            if (baseName == null)
+            {
+                throw new ArgumentNullException(nameof(baseName));
+            }
+
+            if (resourceNamesCache == null)
+            {
+                throw new ArgumentNullException(nameof(resourceNamesCache));
+            }
+
             _resourceAssemblyWrapper = resourceAssemblyWrapper;
             _resourceManager = resourceManager;
             _resourceBaseName = baseName;
@@ -59,20 +83,30 @@ namespace Microsoft.Extensions.Localization
         }
 
         /// <inheritdoc />
-        public virtual LocalizedString this[[NotNull] string name]
+        public virtual LocalizedString this[string name]
         {
             get
             {
+                if (name == null)
+                {
+                    throw new ArgumentNullException(nameof(name));
+                }
+
                 var value = GetStringSafely(name, null);
                 return new LocalizedString(name, value ?? name, resourceNotFound: value == null);
             }
         }
 
         /// <inheritdoc />
-        public virtual LocalizedString this[[NotNull] string name, params object[] arguments]
+        public virtual LocalizedString this[string name, params object[] arguments]
         {
             get
             {
+                if (name == null)
+                {
+                    throw new ArgumentNullException(nameof(name));
+                }
+
                 var format = GetStringSafely(name, null);
                 var value = string.Format(format ?? name, arguments);
                 return new LocalizedString(name, value, resourceNotFound: format == null);
@@ -110,8 +144,13 @@ namespace Microsoft.Extensions.Localization
         /// <param name="includeAncestorCultures"></param>
         /// <param name="culture">The <see cref="CultureInfo"/> to get strings for.</param>
         /// <returns>The strings.</returns>
-        protected IEnumerable<LocalizedString> GetAllStrings(bool includeAncestorCultures, [NotNull] CultureInfo culture)
+        protected IEnumerable<LocalizedString> GetAllStrings(bool includeAncestorCultures, CultureInfo culture)
         {
+            if (culture == null)
+            {
+                throw new ArgumentNullException(nameof(culture));
+            }
+
             var resourceNames = includeAncestorCultures
                 ? GetResourceNamesFromCultureHierarchy(culture)
                 : GetResourceNamesForCulture(culture);
@@ -130,8 +169,13 @@ namespace Microsoft.Extensions.Localization
         /// <param name="name">The name of the string resource.</param>
         /// <param name="culture">The <see cref="CultureInfo"/> to get the string for.</param>
         /// <returns>The resource string, or <c>null</c> if none was found.</returns>
-        protected string GetStringSafely([NotNull] string name, CultureInfo culture)
+        protected string GetStringSafely(string name, CultureInfo culture)
         {
+            if (name == null)
+            {
+                throw new ArgumentNullException(nameof(name));
+            }
+
             var cacheKey = $"name={name}&culture={(culture ?? CultureInfo.CurrentUICulture).Name}";
 
             if (_missingManifestCache.ContainsKey(cacheKey))
diff --git a/src/Microsoft.Extensions.Localization/ResourceManagerStringLocalizerFactory.cs b/src/Microsoft.Extensions.Localization/ResourceManagerStringLocalizerFactory.cs
index 75cac08fde..a77d3a7431 100644
--- a/src/Microsoft.Extensions.Localization/ResourceManagerStringLocalizerFactory.cs
+++ b/src/Microsoft.Extensions.Localization/ResourceManagerStringLocalizerFactory.cs
@@ -6,7 +6,6 @@ using System.IO;
 using System.Reflection;
 using System.Resources;
 using Microsoft.Dnx.Runtime;
-using Microsoft.Extensions.Internal;
 using Microsoft.Extensions.OptionsModel;
 
 namespace Microsoft.Extensions.Localization
@@ -28,9 +27,19 @@ namespace Microsoft.Extensions.Localization
         /// <param name="applicationEnvironment">The <see cref="IApplicationEnvironment"/>.</param>
         /// <param name="localizationOptions">The <see cref="IOptions{LocalizationOptions}"/>.</param>
         public ResourceManagerStringLocalizerFactory(
-            [NotNull] IApplicationEnvironment applicationEnvironment,
-            [NotNull] IOptions<LocalizationOptions> localizationOptions)
+            IApplicationEnvironment applicationEnvironment,
+            IOptions<LocalizationOptions> localizationOptions)
         {
+            if (applicationEnvironment == null)
+            {
+                throw new ArgumentNullException(nameof(applicationEnvironment));
+            }
+
+            if (localizationOptions == null)
+            {
+                throw new ArgumentNullException(nameof(localizationOptions));
+            }
+
             _applicationEnvironment = applicationEnvironment;
             _resourcesRelativePath = localizationOptions.Value.ResourcesPath ?? string.Empty;
             if (!string.IsNullOrEmpty(_resourcesRelativePath))
@@ -46,8 +55,13 @@ namespace Microsoft.Extensions.Localization
         /// </summary>
         /// <param name="resourceSource">The <see cref="Type"/>.</param>
         /// <returns>The <see cref="ResourceManagerStringLocalizer"/>.</returns>
-        public IStringLocalizer Create([NotNull] Type resourceSource)
+        public IStringLocalizer Create(Type resourceSource)
         {
+            if (resourceSource == null)
+            {
+                throw new ArgumentNullException(nameof(resourceSource));
+            }
+
             var typeInfo = resourceSource.GetTypeInfo();
             var assembly = typeInfo.Assembly;
             var baseName = _applicationEnvironment.ApplicationName + "." + _resourcesRelativePath + resourceSource.Name;
@@ -65,8 +79,13 @@ namespace Microsoft.Extensions.Localization
         /// <param name="baseName">The base name of the resource to load strings from.</param>
         /// <param name="location">The location to load resources from.</param>
         /// <returns>The <see cref="ResourceManagerStringLocalizer"/>.</returns>
-        public IStringLocalizer Create([NotNull] string baseName, string location)
+        public IStringLocalizer Create(string baseName, string location)
         {
+            if (baseName == null)
+            {
+                throw new ArgumentNullException(nameof(baseName));
+            }
+
             var rootPath = location ?? _applicationEnvironment.ApplicationName;
             var assembly = Assembly.Load(new AssemblyName(rootPath));
             baseName = rootPath + "." + _resourcesRelativePath + baseName;
diff --git a/src/Microsoft.Extensions.Localization/ResourceManagerWithCultureStringLocalizer.cs b/src/Microsoft.Extensions.Localization/ResourceManagerWithCultureStringLocalizer.cs
index e077bcd682..dda581d5eb 100644
--- a/src/Microsoft.Extensions.Localization/ResourceManagerWithCultureStringLocalizer.cs
+++ b/src/Microsoft.Extensions.Localization/ResourceManagerWithCultureStringLocalizer.cs
@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved. 
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information. 
 
+using System;
 using System.Collections.Generic;
 using System.Globalization;
 using System.Reflection;
@@ -26,31 +27,66 @@ namespace Microsoft.Extensions.Localization
         /// <param name="resourceNamesCache">Cache of the list of strings for a given resource assembly name.</param>
         /// <param name="culture">The specific <see cref="CultureInfo"/> to use.</param>
         public ResourceManagerWithCultureStringLocalizer(
-            [NotNull] ResourceManager resourceManager,
-            [NotNull] Assembly resourceAssembly,
-            [NotNull] string baseName,
-            [NotNull] IResourceNamesCache resourceNamesCache,
-            [NotNull] CultureInfo culture)
+            ResourceManager resourceManager,
+            Assembly resourceAssembly,
+            string baseName,
+            IResourceNamesCache resourceNamesCache,
+            CultureInfo culture)
             : base(resourceManager, resourceAssembly, baseName, resourceNamesCache)
         {
+            if (resourceManager == null)
+            {
+                throw new ArgumentNullException(nameof(resourceManager));
+            }
+
+            if (resourceAssembly == null)
+            {
+                throw new ArgumentNullException(nameof(resourceAssembly));
+            }
+
+            if (baseName == null)
+            {
+                throw new ArgumentNullException(nameof(baseName));
+            }
+
+            if (resourceNamesCache == null)
+            {
+                throw new ArgumentNullException(nameof(resourceNamesCache));
+            }
+
+            if (culture == null)
+            {
+                throw new ArgumentNullException(nameof(culture));
+            }
+
             _culture = culture;
         }
 
         /// <inheritdoc />
-        public override LocalizedString this[[NotNull] string name]
+        public override LocalizedString this[string name]
         {
             get
             {
+                if (name == null)
+                {
+                    throw new ArgumentNullException(nameof(name));
+                }
+
                 var value = GetStringSafely(name, _culture);
                 return new LocalizedString(name, value ?? name);
             }
         }
 
         /// <inheritdoc />
-        public override LocalizedString this[[NotNull] string name, params object[] arguments]
+        public override LocalizedString this[string name, params object[] arguments]
         {
             get
             {
+                if (name == null)
+                {
+                    throw new ArgumentNullException(nameof(name));
+                }
+
                 var format = GetStringSafely(name, _culture);
                 var value = string.Format(_culture, format ?? name, arguments);
                 return new LocalizedString(name, value ?? name, resourceNotFound: format == null);
diff --git a/src/Microsoft.Extensions.Localization/project.json b/src/Microsoft.Extensions.Localization/project.json
index 632e56f762..d4ca2308d4 100644
--- a/src/Microsoft.Extensions.Localization/project.json
+++ b/src/Microsoft.Extensions.Localization/project.json
@@ -5,14 +5,13 @@
         "type": "git",
         "url": "https://github.com/aspnet/localization"
     },
+    "compilationOptions": {
+        "warningsAsErrors": true
+    },
     "dependencies": {
         "Microsoft.Dnx.Runtime.Abstractions": "1.0.0-*",
         "Microsoft.Extensions.DependencyInjection.Abstractions": "1.0.0-*",
         "Microsoft.Extensions.Localization.Abstractions": "1.0.0-*",
-        "Microsoft.Extensions.NotNullAttribute.Sources": {
-            "type": "build",
-            "version": "1.0.0-*"
-        },
         "Microsoft.Extensions.OptionsModel": "1.0.0-*"
     },
     "frameworks": {