diff --git a/glx/glxcmds.c b/glx/glxcmds.c
index f8c3a965c..54d6d7924 100644
--- a/glx/glxcmds.c
+++ b/glx/glxcmds.c
@@ -36,6 +36,7 @@
 #include <X11/extensions/presenttokens.h>
 
 #include "dix/dix_priv.h"
+#include "os/bug_priv.h"
 
 #include "glxserver.h"
 #include <unpack.h>
@@ -122,6 +123,8 @@ validGlxFBConfigForWindow(ClientPtr client, __GLXconfig * config,
         }
     }
 
+    BUG_RETURN_VAL(!pVisual, FALSE);
+
     /* FIXME: What exactly should we check here... */
     if (pVisual->class != glxConvertToXVisualType(config->visualType) ||
         !(config->drawableType & GLX_WINDOW_BIT)) {