diff --git a/src/Microsoft.AspNet.Mvc.Razor/Compilation/SyntaxTreeGenerator.cs b/src/Microsoft.AspNet.Mvc.Razor/Compilation/SyntaxTreeGenerator.cs
index 0453ba051d..606d29376d 100644
--- a/src/Microsoft.AspNet.Mvc.Razor/Compilation/SyntaxTreeGenerator.cs
+++ b/src/Microsoft.AspNet.Mvc.Razor/Compilation/SyntaxTreeGenerator.cs
@@ -27,7 +27,7 @@ namespace Microsoft.AspNet.Mvc.Razor
         {
             return new CSharpParseOptions(
                languageVersion: compilationSettings.LanguageVersion,
-               preprocessorSymbols: compilationSettings.Defines.AsImmutable());
+               preprocessorSymbols: compilationSettings.Defines);
         }
     }
 }
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