diff --git a/lib/libsys/mq_open.2 b/lib/libsys/mq_open.2
--- a/lib/libsys/mq_open.2
+++ b/lib/libsys/mq_open.2
@@ -282,6 +282,20 @@
 or
 .Va mq_msgsize
 was less than or equal to zero.
+.It Bq Er EINVAL
+.Dv O_CREAT
+was specified in
+.Fa oflag ,
+the value of
+.Fa attr
+is not
+.Dv NULL ,
+and
+.Fa mq_maxmsg
+is greater than kern.mqueue.maxmsq
+or
+.Fa mq_msgsize
+is greater than kern.mqueue.maxmsgsize.
 .It Bq Er EMFILE
 Too many message queue descriptors or file descriptors are currently in use
 by this process.
diff --git a/share/man/man4/mqueuefs.4 b/share/man/man4/mqueuefs.4
--- a/share/man/man4/mqueuefs.4
+++ b/share/man/man4/mqueuefs.4
@@ -111,11 +111,25 @@
 To see the queue's attributes, just read the file:
 .Pp
 .Dl "cat /mnt/mqueue/myqueue"
+.Sh SYSCTL VARIABLES
+.Bl -tag -width "kern.features.p1003_1b_mqueue"
+.It Va kern.features.p1003_1b_mqueue
+If mqueuefs support is enabled, this value is 1.
+.It Va kern.mqueue.curmq
+The current number of message queues.
+.It Va kern.mqueue.maxmq
+The maximum number of message queues.
+.It Va kern.mqueue.maxmsgsize
+The maximum size of a message, in bytes.
+.It Va kern.mqueue.maxmsg
+The maximum number of messages in a queue.
+.El
 .Sh SEE ALSO
 .Xr mq_open 2 ,
 .Xr nmount 2 ,
 .Xr unmount 2 ,
 .Xr mount 8 ,
+.Xr sysctl 8 ,
 .Xr umount 8
 .Sh AUTHORS
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