diff --git a/reactos/subsys/win32k/eng/bitblt.c b/reactos/subsys/win32k/eng/bitblt.c
index 33b76c1d097..7f2c7f9c440 100644
--- a/reactos/subsys/win32k/eng/bitblt.c
+++ b/reactos/subsys/win32k/eng/bitblt.c
@@ -16,7 +16,7 @@
  *  along with this program; if not, write to the Free Software
  *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
-/* $Id: bitblt.c,v 1.64 2004/12/14 03:36:46 royce Exp $
+/* $Id: bitblt.c,v 1.65 2004/12/18 17:36:13 royce Exp $
  *
  * COPYRIGHT:        See COPYING in the top level directory
  * PROJECT:          ReactOS kernel
@@ -901,6 +901,9 @@ EngMaskBitBlt(SURFOBJ *DestObj,
   ULONG              Direction;
   POINTL             AdjustedBrushOrigin;
 
+  if ( NULL == Mask )
+    return FALSE;
+
   if (NULL != SourcePoint)
     {
     InputRect.left = SourcePoint->x;