diff --git a/supabase/migrations/00006_ratings_address_check.sql b/supabase/migrations/00006_ratings_address_check.sql
new file mode 100644
index 00000000..39c1e12d
--- /dev/null
+++ b/supabase/migrations/00006_ratings_address_check.sql
@@ -0,0 +1,4 @@
+-- Enforce lowercase hex addresses at the DB level to prevent dedup issues.
+ALTER TABLE ratings
+  ADD CONSTRAINT ratings_rater_address_lowercase
+  CHECK (rater_address = lower(rater_address));