diff --git a/deploy/systemd/privapub-mongod.service b/deploy/systemd/privapub-mongod.service
index 1e13e2a..a074a4e 100644
--- a/deploy/systemd/privapub-mongod.service
+++ b/deploy/systemd/privapub-mongod.service
@@ -7,7 +7,7 @@ Type=exec
 User=www-data
 Group=www-data
 # a one-member replica set (rs0), so a backup reads every collection at one instant; its oplog kept small
-ExecStart=/usr/bin/mongod --dbpath /var/lib/privapub/mongo --port 27022 --bind_ip 127.0.0.1 --noauth --wiredTigerCacheSizeGB 0.25 --replSet rs0 --oplogSizeMB 990 --quiet
+ExecStart=/usr/bin/mongod --dbpath /var/lib/privapub/mongo --port 27022 --bind_ip 127.0.0.1 --noauth --wiredTigerCacheSizeGB 0.25 --replSet rs0 --oplogSize 990 --quiet
 Restart=always
 RestartSec=5
 LimitNOFILE=64000