diff --git a/tools/gif2tiff.c b/tools/gif2tiff.c

index 375b152..2731273 100644

--- a/tools/gif2tiff.c

+++ b/tools/gif2tiff.c

@@ -402,6 +402,10 @@ process(register int code, unsigned char** fill)

     }

     if (oldcode == -1) {

+        if (code >= clear) {

+            fprintf(stderr, "bad input: code=%d is larger than clear=%d\n",code, clear);

+            return 0;

+        }

 	*(*fill)++ = suffix[code];

 	firstchar = oldcode = code;

 	return 1;