diff --git a/lib/log.c b/lib/log.c
index e376205..0914bf8 100644
--- a/lib/log.c
+++ b/lib/log.c
@@ -1036,7 +1036,7 @@
               if (j >= len) /* end of block, not really printing */
                 s += sprintf(s, " ");
 
-              else if(isprint(((char*)mem)[j])) /* printable char */
+              else if(isprint((int)((char*)mem)[j])) /* printable char */
                 s += sprintf(s, "%c", 0xFF & ((char*)mem)[j]);
 
               else /* other char */