diff --git a/sys/conf/files b/sys/conf/files
index 0633223c9a2c..67c01bc646f8 100644
--- a/sys/conf/files
+++ b/sys/conf/files
@@ -2553,6 +2553,7 @@ libkern/strlcpy.c		standard
 libkern/strlen.c		standard
 libkern/strncmp.c		standard
 libkern/strncpy.c		standard
+libkern/strnlen.c		standard
 libkern/strsep.c		standard
 libkern/strspn.c		standard
 libkern/strstr.c		standard
diff --git a/sys/libkern/strnlen.c b/sys/libkern/strnlen.c
new file mode 100644
index 000000000000..805aee8483ff
--- /dev/null
+++ b/sys/libkern/strnlen.c
@@ -0,0 +1,42 @@
+/*-
+ * Copyright (c) 2009 David Schultz <das@FreeBSD.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/libkern.h>
+
+size_t
+strnlen(const char *s, size_t maxlen)
+{
+	size_t len;
+
+	for (len = 0; len < maxlen; len++, s++) {
+		if (!*s)
+			break;
+	}
+	return (len);
+}
diff --git a/sys/sys/libkern.h b/sys/sys/libkern.h
index a6e2acda67e3..65405d049b3e 100644
--- a/sys/sys/libkern.h
+++ b/sys/sys/libkern.h
@@ -116,6 +116,7 @@ size_t	 strlen(const char *);
 int	 strncasecmp(const char *, const char *, size_t);
 int	 strncmp(const char *, const char *, size_t);
 char	*strncpy(char * __restrict, const char * __restrict, size_t);
+size_t	 strnlen(const char *, size_t);
 char	*strsep(char **, const char *delim);
 size_t	 strspn(const char *, const char *);
 char	*strstr(const char *, const char *);