diff --git a/hw/xwin/win.h b/hw/xwin/win.h
index 48795a8b5..3aa158e91 100644
--- a/hw/xwin/win.h
+++ b/hw/xwin/win.h
@@ -1038,6 +1038,9 @@ winCreateMsgWindowThread(void);
 void
 winOS(void);
 
+Bool
+winValidateArgs(void);
+
 /*
  * END DDX and DIX Function Prototypes
  */