diff --git a/src/basic/cgroup-util.h b/src/basic/cgroup-util.h
index c16a33723cc..c549aa4024e 100644
--- a/src/basic/cgroup-util.h
+++ b/src/basic/cgroup-util.h
@@ -34,11 +34,11 @@
 /* An enum of well known cgroup controllers */
 typedef enum CGroupController {
         CGROUP_CONTROLLER_CPU,
-        CGROUP_CONTROLLER_CPUACCT,
-        CGROUP_CONTROLLER_IO,
-        CGROUP_CONTROLLER_BLKIO,
+        CGROUP_CONTROLLER_CPUACCT,    /* v1 only */
+        CGROUP_CONTROLLER_IO,         /* v2 only */
+        CGROUP_CONTROLLER_BLKIO,      /* v1 only */
         CGROUP_CONTROLLER_MEMORY,
-        CGROUP_CONTROLLER_DEVICES,
+        CGROUP_CONTROLLER_DEVICES,    /* v1 only */
         CGROUP_CONTROLLER_PIDS,
         _CGROUP_CONTROLLER_MAX,
         _CGROUP_CONTROLLER_INVALID = -1,