diff --git a/man7/cgroups.7 b/man7/cgroups.7
index 971bfb1ea..68440dfaa 100644
--- a/man7/cgroups.7
+++ b/man7/cgroups.7
@@ -87,6 +87,10 @@ Initially marked experimental, and hidden behind the
 mount option, the new version (cgroups version 2)
 was eventually made official with the release of Linux 4.5.
 Differences between the two versions are described in the text below.
+The file
+.IR cgroup.sane_behavior ,
+present in cgroups v1, is a relic of this mount option. The file
+always reports "0" and is only retained for backward compatibility.
 .PP
 Although cgroups v2 is intended as a replacement for cgroups v1,
 the older system continues to exist