diff --git a/lib/libcasper/services/cap_grp/cap_grp.3 b/lib/libcasper/services/cap_grp/cap_grp.3
index d9e987e8f2d..30aa621ca44 100644
--- a/lib/libcasper/services/cap_grp/cap_grp.3
+++ b/lib/libcasper/services/cap_grp/cap_grp.3
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd February 26, 2018
+.Dd March 18, 2018
 .Dt CAP_GRP 3
 .Os
 .Sh NAME
@@ -70,7 +70,7 @@
 .Ft int
 .Fn cap_grp_limit_fields "cap_channel_t *chan" "const char * const *fields" "size_t nfields"
 .Ft int
-.Fn cap_grp_limit_groups "cap_channel_t *chan" "const char * const *names" "size_t nnames" "gid_t *gids" "size_t ngids"
+.Fn cap_grp_limit_groups "cap_channel_t *chan" "const char * const *names" "size_t nnames" "const gid_t *gids" "size_t ngids"
 .Sh DESCRIPTION
 The functions
 .Fn cap_getgrent ,
@@ -163,7 +163,7 @@ casper service and uses it to get a group name.
 cap_channel_t *capcas, *capgrp;
 const char *cmds[] = { "getgrgid" };
 const char *fields[] = { "gr_name" };
-gid_t gid[] = { 1 };
+const gid_t gid[] = { 1 };
 struct group *group;
 
 /* Open capability to Casper. */
diff --git a/lib/libcasper/services/cap_grp/cap_grp.c b/lib/libcasper/services/cap_grp/cap_grp.c
index 56f16afbfd5..4347f4fbc94 100644
--- a/lib/libcasper/services/cap_grp/cap_grp.c
+++ b/lib/libcasper/services/cap_grp/cap_grp.c
@@ -410,7 +410,7 @@ cap_grp_limit_fields(cap_channel_t *chan, const char * const *fields,
 
 int
 cap_grp_limit_groups(cap_channel_t *chan, const char * const *names,
-    size_t nnames, gid_t *gids, size_t ngids)
+    size_t nnames, const gid_t *gids, size_t ngids)
 {
 	nvlist_t *limits, *groups;
 	unsigned int i;
diff --git a/lib/libcasper/services/cap_grp/cap_grp.h b/lib/libcasper/services/cap_grp/cap_grp.h
index 7c109bcc199..ab755015304 100644
--- a/lib/libcasper/services/cap_grp/cap_grp.h
+++ b/lib/libcasper/services/cap_grp/cap_grp.h
@@ -57,7 +57,7 @@ int cap_grp_limit_cmds(cap_channel_t *chan, const char * const *cmds,
 int cap_grp_limit_fields(cap_channel_t *chan, const char * const *fields,
     size_t nfields);
 int cap_grp_limit_groups(cap_channel_t *chan, const char * const *names,
-    size_t nnames, gid_t *gids, size_t ngids);
+    size_t nnames, const gid_t *gids, size_t ngids);
 #else
 #define	cap_getgrent(chan)		getgrent()
 #define	cap_getgrnam(chan, name)	getgrnam(name)