diff --git a/src/lib/libc/string/swab.3 b/src/lib/libc/string/swab.3
index 77e5a9cc..57afdd4d 100644
--- a/src/lib/libc/string/swab.3
+++ b/src/lib/libc/string/swab.3
@@ -25,9 +25,9 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.\"	$OpenBSD: swab.3,v 1.8 2013/06/05 03:39:23 tedu Exp $
+.\"	$OpenBSD: swab.3,v 1.9 2014/12/12 20:06:13 schwarze Exp $
 .\"
-.Dd $Mdocdate: June 5 2013 $
+.Dd $Mdocdate: December 12 2014 $
 .Dt SWAB 3
 .Os
 .Sh NAME
@@ -36,7 +36,11 @@
 .Sh SYNOPSIS
 .In unistd.h
 .Ft void
-.Fn swab "const void *src" "void *dst" "size_t len"
+.Fo swab
+.Fa "const void *restrict src"
+.Fa "void *restrict dst"
+.Fa "ssize_t len"
+.Fc
 .Sh DESCRIPTION
 The function
 .Fn swab
@@ -48,12 +52,26 @@ to the location referenced by
 .Fa dst ,
 swapping adjacent bytes.
 .Pp
-The argument
+If
 .Fa len
-must be an even number.
+is zero or less,
+.Nm
+does nothing.
+If it is odd, what happens to the last byte is unspecified.
+If
+.Fa src
+and
+.Fa dst
+overlap, behaviour is undefined.
 .Sh SEE ALSO
 .Xr bzero 3 ,
 .Xr memset 3
+.Sh STANDARDS
+The
+.Nm
+function is compliant with the X/Open System Interfaces option of the
+.St -p1003.1-2008
+specification.
 .Sh HISTORY
 The
 .Fn swab