diff --git a/bridgev2/database/upgrades/17-message-mxid-unique.sql b/bridgev2/database/upgrades/17-message-mxid-unique.sql
index 05503191..ee53b3f0 100644
--- a/bridgev2/database/upgrades/17-message-mxid-unique.sql
+++ b/bridgev2/database/upgrades/17-message-mxid-unique.sql
@@ -1,4 +1,5 @@
 -- v17 (compatible with v9+): Add unique constraint for message and reaction mxids
+DELETE FROM message WHERE mxid IN (SELECT mxid FROM message GROUP BY mxid HAVING COUNT(*) > 1);
 -- only: postgres for next 2 lines
 ALTER TABLE message ADD CONSTRAINT message_mxid_unique UNIQUE (bridge_id, mxid);
 ALTER TABLE reaction ADD CONSTRAINT reaction_mxid_unique UNIQUE (bridge_id, mxid);