diff --git a/include/time.h b/include/time.h
index e17feb3b2427..daf8e90c8c66 100644
--- a/include/time.h
+++ b/include/time.h
@@ -121,7 +121,8 @@ double difftime(time_t, time_t);
 struct tm *gmtime(const time_t *);
 struct tm *localtime(const time_t *);
 time_t mktime(struct tm *);
-size_t strftime(char *, size_t, const char *, const struct tm *);
+size_t strftime(char *__restrict, size_t, const char *__restrict,
+    const struct tm *__restrict);
 time_t time(time_t *);
 
 #if __POSIX_VISIBLE
diff --git a/lib/libc/stdtime/strftime.3 b/lib/libc/stdtime/strftime.3
index 172a6a684920..68777753e624 100644
--- a/lib/libc/stdtime/strftime.3
+++ b/lib/libc/stdtime/strftime.3
@@ -47,7 +47,7 @@
 .Sh SYNOPSIS
 .In time.h
 .Ft size_t
-.Fn strftime "char *buf" "size_t maxsize" "const char *format" "const struct tm *timeptr"
+.Fn strftime "char *restrict buf" "size_t maxsize" "const char *restrict format" "const struct tm *restrict timeptr"
 .Sh DESCRIPTION
 The
 .Fn strftime
diff --git a/lib/libc/stdtime/strftime.c b/lib/libc/stdtime/strftime.c
index bd3ba292f8aa..ab50bdcf6ab2 100644
--- a/lib/libc/stdtime/strftime.c
+++ b/lib/libc/stdtime/strftime.c
@@ -44,16 +44,14 @@ static char *	_add(const char *, char *, const char *);
 static char *	_conv(int, const char *, char *, const char *);
 static char *	_fmt(const char *, const struct tm *, char *, const char *);
 
-size_t strftime(char *, size_t, const char *, const struct tm *);
+size_t strftime(char *__restrict, size_t, const char *__restrict,
+    const struct tm *__restrict);
 
 extern char *	tzname[];
 
 size_t
-strftime(s, maxsize, format, t)
-	char *const s;
-	const size_t maxsize;
-	const char *const format;
-	const struct tm *const t;
+strftime(char *__restrict s, size_t maxsize, const char *__restrict format,
+    const struct tm *__restrict t)
 {
 	char *p;