diff --git a/src/mesa/drivers/x11/fakeglx.c b/src/mesa/drivers/x11/fakeglx.c
index 6449dc8..66420f7 100644
--- a/src/mesa/drivers/x11/fakeglx.c
+++ b/src/mesa/drivers/x11/fakeglx.c
@@ -1641,8 +1641,10 @@ Fake_glXQueryExtension( Display *dpy, int *errorb, int *event )
 {
    /* Mesa's GLX isn't really an X extension but we try to act like one. */
    (void) dpy;
-   (void) errorb;
-   (void) event;
+   if (errorb)
+      *errorb = 0;
+   if (event)
+      *event = 0;
    return True;
 }