diff --git a/UpdCheck/main.cpp b/UpdCheck/main.cpp
index 710bff7..7ef954c 100644
--- a/UpdCheck/main.cpp
+++ b/UpdCheck/main.cpp
@@ -23,7 +23,7 @@
 ///
 /// Main function
 ///
-int CALLBACK WinMain(_In_ HINSTANCE hInstance, _In_ HINSTANCE hPrevInstance, _In_ LPSTR lpCmdLine, _In_ int nCmdShow)
+int CALLBACK WinMain(_In_ HINSTANCE hInstance, _In_opt_ HINSTANCE hPrevInstance, _In_ LPSTR lpCmdLine, _In_ int nCmdShow)
 {
     wxApp::CheckBuildOptions(WX_BUILD_OPTIONS_SIGNATURE, "program");