diff --git a/src/Microsoft.AspNetCore.Blazor.Razor.Extensions/BlazorRuntimeNodeWriter.cs b/src/Microsoft.AspNetCore.Blazor.Razor.Extensions/BlazorRuntimeNodeWriter.cs
index a544c10bed..f4b72488b5 100644
--- a/src/Microsoft.AspNetCore.Blazor.Razor.Extensions/BlazorRuntimeNodeWriter.cs
+++ b/src/Microsoft.AspNetCore.Blazor.Razor.Extensions/BlazorRuntimeNodeWriter.cs
@@ -50,6 +50,16 @@ namespace Microsoft.AspNetCore.Blazor.Razor
 
         public override void WriteCSharpCode(CodeRenderingContext context, CSharpCodeIntermediateNode node)
         {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (node == null)
+            {
+                throw new ArgumentNullException(nameof(node));
+            }
+
             var isWhitespaceStatement = true;
             for (var i = 0; i < node.Children.Count; i++)
             {
@@ -63,14 +73,25 @@ namespace Microsoft.AspNetCore.Blazor.Razor
 
             if (isWhitespaceStatement)
             {
+                // The runtime and design time code differ in their handling of whitespace-only
+                // statements. At runtime we can discard them completely. At design time we need
+                // to keep them for the editor.
                 return;
             }
 
+            IDisposable linePragmaScope = null;
+            if (node.Source != null)
+            {
+                linePragmaScope = context.CodeWriter.BuildLinePragma(node.Source.Value);
+                context.CodeWriter.WritePadding(0, node.Source.Value, context);
+            }
+
             for (var i = 0; i < node.Children.Count; i++)
             {
                 if (node.Children[i] is IntermediateToken token && token.IsCSharp)
                 {
                     _scopeStack.IncrementCurrentScopeChildCount(context);
+                    context.AddSourceMappingFor(token);
                     context.CodeWriter.Write(token.Content);
                 }
                 else
@@ -79,6 +100,15 @@ namespace Microsoft.AspNetCore.Blazor.Razor
                     context.RenderNode(node.Children[i]);
                 }
             }
+
+            if (linePragmaScope != null)
+            {
+                linePragmaScope.Dispose();
+            }
+            else
+            {
+                context.CodeWriter.WriteLine();
+            }
         }
 
         public override void WriteCSharpCodeAttributeValue(CodeRenderingContext context, CSharpCodeAttributeValueIntermediateNode node)
diff --git a/test/Microsoft.AspNetCore.Blazor.Build.Test/DeclarationRazorIntegrationTest.cs b/test/Microsoft.AspNetCore.Blazor.Build.Test/DeclarationRazorIntegrationTest.cs
index 555b41f670..e2d29f2e5b 100644
--- a/test/Microsoft.AspNetCore.Blazor.Build.Test/DeclarationRazorIntegrationTest.cs
+++ b/test/Microsoft.AspNetCore.Blazor.Build.Test/DeclarationRazorIntegrationTest.cs
@@ -100,6 +100,62 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
             Assert.Empty(frames);
         }
 
+        [Fact] // Regression test for https://github.com/aspnet/Blazor/issues/453
+        public void DeclarationConfiguration_FunctionsBlockHasLineMappings_MappingsApplyToError()
+        {
+            // Arrange & Act 1
+            var generated = CompileToCSharp(@"
+@functions {
+    public StringBuilder Builder { get; set; }
+}
+");
+
+            // Assert 1
+            AssertSourceEquals(@"
+// <auto-generated/>
+#pragma warning disable 1591
+#pragma warning disable 0414
+#pragma warning disable 0649
+#pragma warning disable 0169
+
+namespace Test
+{
+    #line hidden
+    using System;
+    using System.Collections.Generic;
+    using System.Linq;
+    using System.Threading.Tasks;
+    public class TestComponent : Microsoft.AspNetCore.Blazor.Components.BlazorComponent
+    {
+        #pragma warning disable 1998
+        protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
+        {
+        }
+        #pragma warning restore 1998
+#line 1 ""x:\dir\subdir\Test\TestComponent.cshtml""
+            
+    public StringBuilder Builder { get; set; }
+
+#line default
+#line hidden
+    }
+}
+#pragma warning restore 1591
+", generated);
+
+            // Act 2
+            var assembly = CompileToAssembly(generated, throwOnFailure: false);
+
+            // Assert 2
+            var diagnostic = Assert.Single(assembly.Diagnostics);
+
+            // This error should map to line 2 of the generated file, the test
+            // says 1 because Roslyn's line/column data structures are 0-based.
+            var position = diagnostic.Location.GetMappedLineSpan();
+            Assert.EndsWith(".cshtml", position.Path);
+            Assert.Equal(1, position.StartLinePosition.Line);
+        }
+
         public class BaseClass : BlazorComponent
         {
         }
diff --git a/test/Microsoft.AspNetCore.Blazor.Build.Test/RazorIntegrationTestBase.cs b/test/Microsoft.AspNetCore.Blazor.Build.Test/RazorIntegrationTestBase.cs
index 97b5e3e513..975d7d97c5 100644
--- a/test/Microsoft.AspNetCore.Blazor.Build.Test/RazorIntegrationTestBase.cs
+++ b/test/Microsoft.AspNetCore.Blazor.Build.Test/RazorIntegrationTestBase.cs
@@ -208,7 +208,7 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
             return CompileToAssembly(cSharpResult);
         }
 
-        protected CompileToAssemblyResult CompileToAssembly(CompileToCSharpResult cSharpResult)
+        protected CompileToAssemblyResult CompileToAssembly(CompileToCSharpResult cSharpResult, bool throwOnFailure = true)
         {
             if (cSharpResult.Diagnostics.Any())
             {
@@ -227,10 +227,18 @@ namespace Microsoft.AspNetCore.Blazor.Build.Test
                 .GetDiagnostics()
                 .Where(d => d.Severity != DiagnosticSeverity.Hidden);
 
-            if (diagnostics.Any())
+            if (diagnostics.Any() && throwOnFailure)
             {
                 throw new CompilationFailedException(compilation);
             }
+            else if (diagnostics.Any())
+            {
+                return new CompileToAssemblyResult
+                {
+                    Compilation = compilation,
+                    Diagnostics = diagnostics,
+                };
+            }
 
             using (var peStream = new MemoryStream())
             {
diff --git a/test/Microsoft.AspNetCore.Blazor.Build.Test/RuntimeCodeGenerationRazorIntegrationTest.cs b/test/Microsoft.AspNetCore.Blazor.Build.Test/RuntimeCodeGenerationRazorIntegrationTest.cs
index db989dac4c..b6d346e3cc 100644
--- a/test/Microsoft.AspNetCore.Blazor.Build.Test/RuntimeCodeGenerationRazorIntegrationTest.cs
+++ b/test/Microsoft.AspNetCore.Blazor.Build.Test/RuntimeCodeGenerationRazorIntegrationTest.cs
@@ -49,6 +49,7 @@ namespace Test
         protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
         {
             base.BuildRenderTree(builder);
+
             builder.OpenComponent<Test.MyComponent>(0);
             builder.CloseComponent();
         }
@@ -110,6 +111,7 @@ namespace Test
         protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
         {
             base.BuildRenderTree(builder);
+
             builder.OpenComponent<Test.MyComponent>(0);
             builder.AddAttribute(1, ""IntProperty"", 123);
             builder.AddAttribute(2, ""BoolProperty"", true);
@@ -164,6 +166,7 @@ namespace Test
         protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
         {
             base.BuildRenderTree(builder);
+
             builder.OpenComponent<Test.MyComponent>(0);
             builder.AddAttribute(1, ""StringProperty"", 42.ToString());
             builder.CloseComponent();
@@ -214,6 +217,7 @@ namespace Test
         protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
         {
             base.BuildRenderTree(builder);
+
             builder.OpenComponent<Test.MyComponent>(0);
             builder.AddAttribute(1, ""some-attribute"", ""foo"");
             builder.AddAttribute(2, ""another-attribute"", 43.ToString());
@@ -276,20 +280,26 @@ namespace Test
         protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
         {
             base.BuildRenderTree(builder);
+
             builder.OpenComponent<Test.MyComponent>(0);
             builder.AddAttribute(1, ""OnClick"", new Microsoft.AspNetCore.Blazor.UIEventHandler(e => { Increment(); }));
             builder.CloseComponent();
             builder.AddContent(2, ""\n\n"");
         }
         #pragma warning restore 1998
-        
+#line 4 ""x:\dir\subdir\Test\TestComponent.cshtml""
+            
     private int counter;
     private void Increment() {
         counter++;
     }
+
+#line default
+#line hidden
     }
 }
 #pragma warning restore 1591
+
 ", generated);
         }
 
@@ -344,20 +354,26 @@ namespace Test
         protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
         {
             base.BuildRenderTree(builder);
+
             builder.OpenComponent<Test.MyComponent>(0);
             builder.AddAttribute(1, ""OnClick"", new Microsoft.AspNetCore.Blazor.UIEventHandler(Increment));
             builder.CloseComponent();
             builder.AddContent(2, ""\n\n"");
         }
         #pragma warning restore 1998
-        
+#line 5 ""x:\dir\subdir\Test\TestComponent.cshtml""
+            
     private int counter;
     private void Increment(UIEventArgs e) {
         counter++;
     }
+
+#line default
+#line hidden
     }
 }
 #pragma warning restore 1591
+
 ", generated);
         }
 
@@ -404,6 +420,7 @@ namespace Test
         protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
         {
             base.BuildRenderTree(builder);
+
             builder.OpenComponent<Test.MyComponent>(0);
             builder.AddAttribute(1, ""MyAttr"", ""abc"");
             builder.AddAttribute(2, ""ChildContent"", (Microsoft.AspNetCore.Blazor.RenderFragment)((builder2) => {
@@ -466,6 +483,7 @@ namespace Test
         protected override void BuildRenderTree(Microsoft.AspNetCore.Blazor.RenderTree.RenderTreeBuilder builder)
         {
             base.BuildRenderTree(builder);
+
             builder.OpenComponent<Test.MyComponent>(0);
             builder.CloseComponent();
         }