diff --git a/libc/arch-riscv64/string/strnlen.c b/libc/arch-riscv64/string/strnlen.c
new file mode 100644
index 0000000..0e31c3b
--- /dev/null
+++ b/libc/arch-riscv64/string/strnlen.c
@@ -0,0 +1,32 @@
+/*	$OpenBSD: strnlen.c,v 1.9 2019/01/25 00:19:25 millert Exp $	*/
+
+/*
+ * Copyright (c) 2010 Todd C. Miller <millert@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <sys/types.h>
+
+#include <string.h>
+
+size_t
+strnlen_gc(const char *str, size_t maxlen)
+{
+	const char *cp;
+
+	for (cp = str; maxlen != 0 && *cp != '\0'; cp++, maxlen--)
+		;
+
+	return (size_t)(cp - str);
+}