diff --git a/inventory/group_vars/odcs-backend-stg b/inventory/group_vars/odcs-backend-stg
index 18cea4f6cd..055241592a 100644
--- a/inventory/group_vars/odcs-backend-stg
+++ b/inventory/group_vars/odcs-backend-stg
@@ -35,6 +35,9 @@ custom_rules: [ '-A INPUT -p tcp -m tcp -s 10.5.126.13 --dport 873 -j ACCEPT', '
 
 fas_client_groups: sysadmin-noc,sysadmin-releng,sysadmin-mbs,sysadmin-veteran
 
+# Set very low memory limit, for testing.
+fedmsg_hub_memory_limit: 10M
+
 # These are consumed by a task in roles/fedmsg/base/main.yml
 fedmsg_certs:
 - service: odcs
diff --git a/roles/fedmsg/hub/defaults/main.yml b/roles/fedmsg/hub/defaults/main.yml
index 4f0428de67..5777dc3db9 100644
--- a/roles/fedmsg/hub/defaults/main.yml
+++ b/roles/fedmsg/hub/defaults/main.yml
@@ -1,7 +1,9 @@
 # This is false by default.  You have to override it when including the role.
 enable_websocket_server: False
 
-# Absolute memory limit in MB for fedmsg-hub.service. Zero means infinity.
+# Absolute memory limit in bytes for fedmsg-hub and fedmsg-bub-3
+# services.  The value the value can be suffixed with K, M, G or T.
+# Zero means infinity (no limit).
 fedmsg_hub_memory_limit: 0
 
 # Restart fedmsg-hub.service on failure.