diff --git a/glx/glxext.c b/glx/glxext.c
index 9b4d81641..d39fe6d8e 100644
--- a/glx/glxext.c
+++ b/glx/glxext.c
@@ -293,6 +293,7 @@ glxClientCallback(CallbackListPtr *list, void *closure, void *data)
         free(cl->returnBuf);
         free(cl->largeCmdBuf);
         free(cl->GLClientextensions);
+        memset(cl, 0, sizeof(*cl));
         break;
 
     default: