diff --git a/man2/flock.2 b/man2/flock.2
index 2e38a9d08..2dce918b0 100644
--- a/man2/flock.2
+++ b/man2/flock.2
@@ -223,6 +223,8 @@ and
 locks
 .I do
 interact with one another over NFS.
+It also means that in order to place an exclusive lock,
+the file must be opened for writing.
 .PP
 Since Linux 2.6.37,
 .\" commit 5eebde23223aeb0ad2d9e3be6590ff8bbfab0fc2