diff --git a/man3/strlen.3 b/man3/strlen.3
index e0657193b..9f431b03a 100644
--- a/man3/strlen.3
+++ b/man3/strlen.3
@@ -60,7 +60,7 @@ T{
 T}	Thread safety	MT-Safe
 .TE
 .SH CONFORMING TO
-SVr4, 4.3BSD, C89, C99.
+POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
 .SH SEE ALSO
 .BR string (3),
 .BR strnlen (3),