diff --git "a/win32ss/reactx/ntddraw/dxeng.c" "b/win32ss/reactx/ntddraw/dxeng.c"
index 10c4b9937cb..8951d922c5a 100644
--- "a/win32ss/reactx/ntddraw/dxeng.c"
+++ "b/win32ss/reactx/ntddraw/dxeng.c"
@@ -535,6 +535,9 @@ DxEngLockHdev(HDEV hDev)
 
     DPRINT("hDev: %p\n", hDev);
 
+    if (!hDev)
+        return FALSE;
+
     Resource = (PERESOURCE)ppdev->hsemDevLock;
 
     if (Resource)