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
@@ -45,6 +45,7 @@
 .Lb librt
 .Sh SYNOPSIS
 .In mqueue.h
+.In fnctl.h
 .Ft mqd_t
 .Fn mq_open "const char *name" "int oflag" "..."
 .Sh DESCRIPTION