diff --git a/man2/msgop.2 b/man2/msgop.2
index badb0fefa..0a230d1a2 100644
--- a/man2/msgop.2
+++ b/man2/msgop.2
@@ -398,6 +398,13 @@ was specified in
 and no message of the requested type existed on the message queue.
 .SH CONFORMING TO
 SVr4, POSIX.1-2001.
+
+The
+.B MSG_EXCEPT
+flag is Linux-specific;
+its definition can be obtained by defining the
+.B _GNU_SOURCE
+feature test macro.
 .SH NOTES
 The inclusion of
 .I <sys/types.h>