diff --git a/src/Microsoft.AspNet.Cors/CorsPolicyBuilder.cs b/src/Microsoft.AspNet.Cors/CorsPolicyBuilder.cs
index 71b500cd48..d018b92a68 100644
--- a/src/Microsoft.AspNet.Cors/CorsPolicyBuilder.cs
+++ b/src/Microsoft.AspNet.Cors/CorsPolicyBuilder.cs
@@ -180,7 +180,11 @@ namespace Microsoft.AspNet.Cors.Infrastructure
             WithHeaders(policy.Headers.ToArray());
             WithExposedHeaders(policy.ExposedHeaders.ToArray());
             WithMethods(policy.Methods.ToArray());
-            SetPreflightMaxAge(policy.PreflightMaxAge.Value);
+
+            if (policy.PreflightMaxAge.HasValue)
+            {
+                SetPreflightMaxAge(policy.PreflightMaxAge.Value);
+            }
 
             if (policy.SupportsCredentials)
             {
diff --git a/test/Microsoft.AspNet.Cors.Test/CorsPolicyBuilderTests.cs b/test/Microsoft.AspNet.Cors.Test/CorsPolicyBuilderTests.cs
index c16a71aee3..5f9f6fe737 100644
--- a/test/Microsoft.AspNet.Cors.Test/CorsPolicyBuilderTests.cs
+++ b/test/Microsoft.AspNet.Cors.Test/CorsPolicyBuilderTests.cs
@@ -14,16 +14,16 @@ namespace Microsoft.AspNet.Cors.Infrastructure
         public void Constructor_WithPolicy_AddsTheGivenPolicy()
         {
             // Arrange
-            var policy = new CorsPolicy();
-            policy.Origins.Add("http://existing.com");
-            policy.Headers.Add("Existing");
-            policy.Methods.Add("GET");
-            policy.ExposedHeaders.Add("ExistingExposed");
-            policy.SupportsCredentials = true;
-            policy.PreflightMaxAge = TimeSpan.FromSeconds(12);
+            var originalPolicy = new CorsPolicy();
+            originalPolicy.Origins.Add("http://existing.com");
+            originalPolicy.Headers.Add("Existing");
+            originalPolicy.Methods.Add("GET");
+            originalPolicy.ExposedHeaders.Add("ExistingExposed");
+            originalPolicy.SupportsCredentials = true;
+            originalPolicy.PreflightMaxAge = TimeSpan.FromSeconds(12);
 
             // Act
-            var builder = new CorsPolicyBuilder(policy);
+            var builder = new CorsPolicyBuilder(originalPolicy);
 
             // Assert
             var corsPolicy = builder.Build();
@@ -32,13 +32,41 @@ namespace Microsoft.AspNet.Cors.Infrastructure
             Assert.False(corsPolicy.AllowAnyMethod);
             Assert.False(corsPolicy.AllowAnyOrigin);
             Assert.True(corsPolicy.SupportsCredentials);
-            Assert.Equal(policy.Headers, corsPolicy.Headers);
-            Assert.Equal(policy.Methods, corsPolicy.Methods);
-            Assert.Equal(policy.Origins, corsPolicy.Origins);
-            Assert.Equal(policy.ExposedHeaders, corsPolicy.ExposedHeaders);
+            Assert.NotSame(originalPolicy.Headers, corsPolicy.Headers);
+            Assert.Equal(originalPolicy.Headers, corsPolicy.Headers);
+            Assert.NotSame(originalPolicy.Methods, corsPolicy.Methods);
+            Assert.Equal(originalPolicy.Methods, corsPolicy.Methods);
+            Assert.NotSame(originalPolicy.Origins, corsPolicy.Origins);
+            Assert.Equal(originalPolicy.Origins, corsPolicy.Origins);
+            Assert.NotSame(originalPolicy.ExposedHeaders, corsPolicy.ExposedHeaders);
+            Assert.Equal(originalPolicy.ExposedHeaders, corsPolicy.ExposedHeaders);
             Assert.Equal(TimeSpan.FromSeconds(12), corsPolicy.PreflightMaxAge);
         }
 
+        [Fact]
+        public void ConstructorWithPolicy_HavingNullPreflightMaxAge_AddsTheGivenPolicy()
+        {
+            // Arrange
+            var originalPolicy = new CorsPolicy();
+            originalPolicy.Origins.Add("http://existing.com");
+
+            // Act
+            var builder = new CorsPolicyBuilder(originalPolicy);
+
+            // Assert
+            var corsPolicy = builder.Build();
+
+            Assert.Null(corsPolicy.PreflightMaxAge);
+            Assert.False(corsPolicy.AllowAnyHeader);
+            Assert.False(corsPolicy.AllowAnyMethod);
+            Assert.False(corsPolicy.AllowAnyOrigin);
+            Assert.NotSame(originalPolicy.Origins, corsPolicy.Origins);
+            Assert.Equal(originalPolicy.Origins, corsPolicy.Origins);
+            Assert.Empty(corsPolicy.Headers);
+            Assert.Empty(corsPolicy.Methods);
+            Assert.Empty(corsPolicy.ExposedHeaders);
+        }
+
         [Fact]
         public void Constructor_WithNoOrigin()
         {
@@ -112,7 +140,6 @@ namespace Microsoft.AspNet.Cors.Infrastructure
             Assert.Equal(new List<string>() { "*" }, corsPolicy.Origins);
         }
 
-
         [Fact]
         public void WithMethods_AddsMethods()
         {