diff --git a/lib/constants.py b/lib/constants.py
index ccfa24a78a5104d638f1cca024c1ac9d6b19f7ca..e629175e1e2f03b960492d02910ef1d3cfdd02fb 100644
--- a/lib/constants.py
+++ b/lib/constants.py
@@ -423,7 +423,6 @@ DRBD_VALID_BARRIER_OPT = frozenset([
   frozenset([DRBD_B_DISK_DRAIN]),
   frozenset([DRBD_B_DISK_FLUSH]),
   frozenset([DRBD_B_DISK_DRAIN, DRBD_B_DISK_FLUSH]),
-  frozenset([DRBD_B_DISK_DRAIN, DRBD_B_DISK_FLUSH]),
   frozenset([DRBD_B_DISK_BARRIERS, DRBD_B_DISK_DRAIN]),
   frozenset([DRBD_B_DISK_BARRIERS, DRBD_B_DISK_FLUSH]),
   frozenset([DRBD_B_DISK_BARRIERS, DRBD_B_DISK_FLUSH, DRBD_B_DISK_DRAIN]),