diff --git a/glx/glxcmds.c b/glx/glxcmds.c
index e0890e982b..9458587b7f 100644
--- a/glx/glxcmds.c
+++ b/glx/glxcmds.c
@@ -2195,6 +2195,9 @@ __glXDisp_RenderLarge(__GLXclientState * cl, GLbyte * pc)
             return BadLength;
         }
 
+        if (dataBytes > cmdlen)
+            return BadLength;
+
         /*
          ** Make enough space in the buffer, then copy the entire request.
          */