diff --git a/lib/strnlen.c b/lib/strnlen.c
index 5a03d7ec942..155a594fccd 100644
--- a/lib/strnlen.c
+++ b/lib/strnlen.c
@@ -25,9 +25,10 @@
 size_t
 strnlen (const char *s, size_t maxlen)
 {
+  size_t i = 0;
   /* Do not use memchr, because on some platforms memchr has
      undefined behavior if MAXLEN exceeds the number of bytes in S.  */
-  for (size_t i = 0; i < maxlen && s[i]; i++)
+  for (; i < maxlen && s[i]; i++)
     continue;
   return i;
 }