--- tk/generic/tkImgGIF.c.orig	2008-02-09 16:44:04.000000000 -0800
+++ tk/generic/tkImgGIF.c	2008-02-09 16:47:47.000000000 -0800
@@ -804,6 +804,12 @@
 		Tcl_PosixError(interp), (char *) NULL);
 	return TCL_ERROR;
     }
+
+    if (initialCodeSize > MAX_LWZ_BITS) {
+    	Tcl_SetResult(interp, "malformed image", TCL_STATIC);
+	return TCL_ERROR;
+    }
+
     if (transparent!=-1) {
 	cmap[transparent][CM_RED] = 0;
 	cmap[transparent][CM_GREEN] = 0;