diff --git a/win32ss/gdi/eng/pdevobj.c b/win32ss/gdi/eng/pdevobj.c
index eb05e237039..a9f959b4b23 100644
--- a/win32ss/gdi/eng/pdevobj.c
+++ b/win32ss/gdi/eng/pdevobj.c
@@ -365,6 +365,7 @@ EngpCreatePDEV(
     }
     else
     {
+        ASSERT(gpPrimaryGraphicsDevice);
         pGraphicsDevice = gpPrimaryGraphicsDevice;
     }