1 files changed, 5 insertions, 1 deletions
diff --git a/utf8.c b/utf8.c
index 24dc69297b..f65c94fbc7 100644
--- a/utf8.c
+++ b/utf8.c
@@ -163,9 +163,13 @@ bool
 Perl_is_utf8_string(pTHX_ U8 *s, STRLEN len)
 {
     U8* x = s;
-    U8* send = s + len;
+    U8* send;
     STRLEN c;
 
+    if (!len)
+	len = strlen(s);
+    send = s + len;
+
     while (x < send) {
         c = is_utf8_char(x);
 	if (!c)