diff --git a/src/libdraw/stringwidth.c b/src/libdraw/stringwidth.c
index f0d1372..8d8c6d0 100644
--- a/src/libdraw/stringwidth.c
+++ b/src/libdraw/stringwidth.c
@@ -25,7 +25,7 @@
 	}else
 		rptr = &r;
 	twid = 0;
-	while(len && (*s || *r)){
+	while(len>0 && (*s || *r)){
 		max = Max;
 		if(len < max)
 			max = len;