diff --git a/build.cake b/build.cake
index a52a8a912e..d568515bac 100644
--- a/build.cake
+++ b/build.cake
@@ -398,7 +398,7 @@ void BuildFramework(string configuration, string framework)
 		case "sl-5.0":
 			BuildProject("src/NUnitFramework/framework/nunit.framework-sl-5.0.csproj", configuration, MSBuildPlatform.x86);
 			BuildProject("src/NUnitFramework/nunitlite/nunitlite-sl-5.0.csproj", configuration, MSBuildPlatform.x86);
-			BuildProject("src/NUnitFramework/mock-assembly/mock-assembly-sl-5.0.csproj", configuration);
+			BuildProject("src/NUnitFramework/mock-assembly/mock-assembly-sl-5.0.csproj", configuration, MSBuildPlatform.x86);
 			BuildProject("src/NUnitFramework/testdata/nunit.testdata-sl-5.0.csproj", configuration, MSBuildPlatform.x86);
 			BuildProject("src/NUnitFramework/tests/nunit.framework.tests-sl-5.0.csproj", configuration, MSBuildPlatform.x86);
 			BuildProject("src/NUnitFramework/nunitlite.tests/nunitlite.tests-sl-5.0.csproj", configuration, MSBuildPlatform.x86);