diff --git a/lib/libc/string/strndup.c b/lib/libc/string/strndup.c
index 56aa6a83a2e..abb1e030eee 100644
--- a/lib/libc/string/strndup.c
+++ b/lib/libc/string/strndup.c
@@ -42,9 +42,7 @@ strndup(const char *str, size_t n)
 	size_t len;
 	char *copy;
 
-	for (len = 0; len < n && str[len]; len++)
-		continue;
-
+	len = strnlen(str, n);
 	if ((copy = malloc(len + 1)) == NULL)
 		return (NULL);
 	memcpy(copy, str, len);