diff --git a/man2/setns.2 b/man2/setns.2
index 18e802023..5985c099b 100644
--- a/man2/setns.2
+++ b/man2/setns.2
@@ -131,8 +131,12 @@ capabilities in its own user namespace and
 .BR CAP_SYS_ADMIN
 in the user namespace that owns the target mount namespace.
 .IP
-A process may not be reassociated with a new mount namespace if it is
-multithreaded.
+A process can't join a new mount namespace if it is sharing
+filesystem-related attributes
+(the attributes whose sharing is controlled by the
+.BR clone (2)
+.B CLONE_FS
+flag) with another process.
 .\" Above check is in fs/namespace.c:mntns_install() [3.8 source]
 .IP
 See