diff --git a/man7/cgroups.7 b/man7/cgroups.7
index 91fd650bb..f23fbcb0d 100644
--- a/man7/cgroups.7
+++ b/man7/cgroups.7
@@ -679,6 +679,15 @@ echo '+pids -memory' > x/y/cgroup.subtree_control
 .in
 .IP
 .PP
+An attempt to enable a controller
+that is not present in
+.I cgroup.controllers
+leads to an
+.B ENOENT
+error when writing to the
+.I cgroup.subtree_control
+file.
+.PP
 Because the list of controllers in
 .I cgroup.subtree_control
 is a subset of those