diff --git a/Src/Newtonsoft.Json/Newtonsoft.Json.WinRT.csproj b/Src/Newtonsoft.Json/Newtonsoft.Json.WinRT.csproj
index d52a0f08..3f502a45 100644
--- a/Src/Newtonsoft.Json/Newtonsoft.Json.WinRT.csproj
+++ b/Src/Newtonsoft.Json/Newtonsoft.Json.WinRT.csproj
@@ -155,6 +155,7 @@
     <Compile Include="JsonConverterCollection.cs" />
     <Compile Include="JsonDictionaryAttribute.cs" />
     <Compile Include="JsonException.cs" />
+    <Compile Include="JsonExtensionDataAttribute.cs" />
     <Compile Include="JsonIgnoreAttribute.cs" />
     <Compile Include="JsonObjectAttribute.cs" />
     <Compile Include="JsonPosition.cs" />