diff --git a/msix/storeapi/storeapi.vcxproj b/msix/storeapi/storeapi.vcxproj
index c98886514..8c063c59d 100644
--- a/msix/storeapi/storeapi.vcxproj
+++ b/msix/storeapi/storeapi.vcxproj
@@ -43,9 +43,11 @@
     <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
   </ImportGroup>
   <PropertyGroup Label="UserMacros" />
-  <PropertyGroup Label="Mock API" Condition="'$(UP4W_TEST_WITH_MS_STORE_MOCK)' == ''">
-    <DefineConstants>UP4W_TEST_WITH_MS_STORE_MOCK</DefineConstants>
-  </PropertyGroup>
+  <ItemDefinitionGroup Label="Mock API" Condition="'$(UP4W_TEST_WITH_MS_STORE_MOCK)' != ''">
+    <ClCompile>
+      <PreprocessorDefinitions>UP4W_TEST_WITH_MS_STORE_MOCK;%(PreProcessorDefinitions)</PreprocessorDefinitions>
+    </ClCompile>
+  </ItemDefinitionGroup>
   <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
     <ClCompile>
       <WarningLevel>Level3</WarningLevel>