diff --git a/windows/winproc.c b/windows/winproc.c
index e8946ee..d7a196a 100644
--- a/windows/winproc.c
+++ b/windows/winproc.c
@@ -235,6 +235,7 @@
  */
 WNDPROC16 WINPROC_GetProc( HWINDOWPROC proc, WINDOWPROCTYPE type )
 {
+    if (!proc) return NULL;
     if (type == WIN_PROC_16)  /* We want a 16:16 address */
     {
         if (((WINDOWPROC *)proc)->type == WIN_PROC_16)