diff --git a/share/man/man9/groupmember.9 b/share/man/man9/groupmember.9
index d447bf64c482..3a516622efce 100644
--- a/share/man/man9/groupmember.9
+++ b/share/man/man9/groupmember.9
@@ -1,58 +1,64 @@
 .\"
 .\" Copyright (C) 2001 Chad David <davidc@acns.ab.ca>. All rights reserved.
+.\" Copyright (C) 2023 Olivier Certner <olce.freebsd@certner.fr>
 .\"
 .\" 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(s), this list of conditions and the following disclaimer as
 .\"    the first lines of this file unmodified other than the possible
 .\"    addition of one or more copyright notices.
 .\" 2. Redistributions in binary form must reproduce the above copyright
 .\"    notice(s), 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 COPYRIGHT HOLDER(S) ``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 COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
 .\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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 .\"
-.Dd July 9, 2001
+.Dd August 18, 2023
 .Dt GROUPMEMBER 9
 .Os
 .Sh NAME
 .Nm groupmember
-.Nd checks group set for a group ID
+.Nd checks if credentials mandate some group membership
 .Sh SYNOPSIS
 .In sys/param.h
 .In sys/ucred.h
 .Ft int
 .Fn groupmember "gid_t gid" "struct ucred *cred"
 .Sh DESCRIPTION
 The
 .Fn groupmember
-function checks to see if the given
-.Fa gid
-is in the group set of the credentials.
+function checks if credentials
+.Fa cred
+indicate that the associated subject or object is a member of the group
+designated by the group ID
+.Fa gid .
 .Pp
-Its arguments are:
-.Bl -tag -width ".Fa cred"
-.It Fa gid
-The group ID to check for.
-.It Fa cred
-The credentials to search for the group in.
-.El
+Considered groups in
+.Fa cred
+are the effective and supplementary groups.
+The real group is not taken into account.
 .Sh RETURN VALUES
 If the
 .Fa gid
-is found, 1 is returned; otherwise, 0 is returned.
+is found, 1 is returned, otherwise 0.
+.Sh SEE ALSO
+.Xr getgroups 2
+.Xr setgroups 2
 .Sh AUTHORS
-This manual page was written by
-.An Chad David Aq Mt davidc@acns.ab.ca .
+This manual page was initially written by
+.An -nosplit
+.An Chad David Aq Mt davidc@acns.ab.ca
+and was revised by
+.An Olivier Certner Aq Mt olce.freebsd@certner.fr .