diff --git a/src/mesa/drivers/x11/fakeglx.c b/src/mesa/drivers/x11/fakeglx.c
index 1bab6d91a41..98003b08581 100644
--- a/src/mesa/drivers/x11/fakeglx.c
+++ b/src/mesa/drivers/x11/fakeglx.c
@@ -1727,6 +1727,9 @@ Fake_glXGetConfig( Display *dpy, XVisualInfo *visinfo,
 {
    XMesaVisual xmvis;
 
+   if (!dpy || !visInfo)
+      return GLX_BAD_ATTRIBUTE;
+
    xmvis = find_glx_visual( dpy, visinfo );
    if (!xmvis) {
       /* this visual wasn't obtained with glXChooseVisual */