diff --git a/tools/convbdf.c b/tools/convbdf.c
index 513b1d7007..010e8ee2c2 100644
--- a/tools/convbdf.c
+++ b/tools/convbdf.c
@@ -737,8 +737,8 @@ int rotleft(unsigned char *dst, /* output buffer */
     src_words = BITMAP_WORDS(width) * height;
 
     if(((height + 7) / 8) * width > dstlen) {
-        fprintf(stderr, "%s:%d %d x %d overflows %d bytes buffer, needs %d\n",
-                __FILE__, __LINE__, width, height, (int)dstlen,
+        fprintf(stderr, "%s:%d %d x %d overflows %ld bytes buffer, needs %d\n",
+                __FILE__, __LINE__, width, height, (unsigned long)dstlen,
                 ((height + 7) / 8) * width );
         return 0;
     }