diff --git a/src/Microsoft.AspNet.Hosting/Properties/AssemblyInfo.cs b/src/Microsoft.AspNet.Hosting/Properties/AssemblyInfo.cs
index 025a94598c..6145905b3a 100644
--- a/src/Microsoft.AspNet.Hosting/Properties/AssemblyInfo.cs
+++ b/src/Microsoft.AspNet.Hosting/Properties/AssemblyInfo.cs
@@ -2,5 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.Reflection;
+using System.Runtime.CompilerServices;
 
-[assembly: AssemblyMetadata("Serviceable", "True")]
\ No newline at end of file
+[assembly: AssemblyMetadata("Serviceable", "True")]
+[assembly: InternalsVisibleTo("Microsoft.AspNet.Hosting.Tests")]
diff --git a/src/Microsoft.AspNet.Hosting/WebHostBuilder.cs b/src/Microsoft.AspNet.Hosting/WebHostBuilder.cs
index 4ae42e9c46..052f4740c1 100644
--- a/src/Microsoft.AspNet.Hosting/WebHostBuilder.cs
+++ b/src/Microsoft.AspNet.Hosting/WebHostBuilder.cs
@@ -42,8 +42,10 @@ namespace Microsoft.AspNet.Hosting
         private string _serverFactoryLocation;
         private IServerFactory _serverFactory;
 
-        public WebHostBuilder([NotNull] IServiceProvider services) 
-            : this(services, config: new ConfigurationBuilder().Build()) { }
+        public WebHostBuilder([NotNull] IServiceProvider services)
+            : this(services, config: new ConfigurationBuilder().Build())
+        {
+        }
 
         public WebHostBuilder([NotNull] IServiceProvider services, [NotNull] IConfiguration config)
         {
@@ -109,7 +111,7 @@ namespace Microsoft.AspNet.Hosting
             // Only one of these should be set, but they are used in priority
             engine.Startup = _startup;
             engine.StartupType = _startupType;
-            engine.StartupAssemblyName = _config.Get(ApplicationKey) ?? _config.Get(OldApplicationKey) ?? appEnvironment.ApplicationName;
+            engine.StartupAssemblyName = _startupAssemblyName ?? _config.Get(ApplicationKey) ?? _config.Get(OldApplicationKey) ?? appEnvironment.ApplicationName;
 
             return engine;
         }
@@ -177,7 +179,8 @@ namespace Microsoft.AspNet.Hosting
         public WebHostBuilder UseStartup([NotNull] Action<IApplicationBuilder> configureApp, Action<IServiceCollection> configureServices)
         {
             _startup = new StartupMethods(configureApp,
-                services => {
+                services =>
+                {
                     if (configureServices != null)
                     {
                         configureServices(services);
@@ -187,4 +190,4 @@ namespace Microsoft.AspNet.Hosting
             return this;
         }
     }
-}
\ No newline at end of file
+}
diff --git a/test/Microsoft.AspNet.Hosting.Tests/WebHostBuilderTests.cs b/test/Microsoft.AspNet.Hosting.Tests/WebHostBuilderTests.cs
new file mode 100644
index 0000000000..94cf636d9c
--- /dev/null
+++ b/test/Microsoft.AspNet.Hosting.Tests/WebHostBuilderTests.cs
@@ -0,0 +1,34 @@
+// 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.AspNet.Hosting.Internal;
+using Microsoft.Framework.Runtime.Infrastructure;
+using Xunit;
+
+namespace Microsoft.AspNet.Hosting
+{
+    public class WebHostBuilderTests
+    {
+        [Fact]
+        public void Build_uses_application_for_startup_assembly_by_default()
+        {
+            var builder = CreateWebHostBuilder();
+
+            var engine = (HostingEngine)builder.Build();
+
+            Assert.Equal("Microsoft.AspNet.Hosting.Tests", engine.StartupAssemblyName);
+        }
+
+        [Fact]
+        public void Build_honors_UseStartup_with_string()
+        {
+            var builder = CreateWebHostBuilder();
+
+            var engine = (HostingEngine)builder.UseStartup("MyStartupAssembly").Build();
+
+            Assert.Equal("MyStartupAssembly", engine.StartupAssemblyName);
+        }
+
+        private WebHostBuilder CreateWebHostBuilder() => new WebHostBuilder(CallContextServiceLocator.Locator.ServiceProvider);
+    }
+}