diff --git a/libs/@local/graph/migrations/graph-migrations/v009__entities/up.sql b/libs/@local/graph/migrations/graph-migrations/v009__entities/up.sql
index 57865c0633a..5da96dbbf5a 100644
--- a/libs/@local/graph/migrations/graph-migrations/v009__entities/up.sql
+++ b/libs/@local/graph/migrations/graph-migrations/v009__entities/up.sql
@@ -19,6 +19,10 @@ CREATE TABLE entity_ids (
     )
 );
 
+-- An entity UUID identifies an entity across all webs, not only within its web.
+CREATE UNIQUE INDEX entity_ids_entity_uuid
+ON entity_ids (entity_uuid);
+
 CREATE INDEX entity_ids_created_at_transaction_time
 ON entity_ids (created_at_transaction_time);
 CREATE INDEX entity_ids_created_at_decision_time
diff --git a/libs/@local/graph/postgres-store/postgres_migrations/V64__entity_uuid_unique.sql b/libs/@local/graph/postgres-store/postgres_migrations/V64__entity_uuid_unique.sql
new file mode 100644
index 00000000000..15a0f5a4aae
--- /dev/null
+++ b/libs/@local/graph/postgres-store/postgres_migrations/V64__entity_uuid_unique.sql
@@ -0,0 +1,3 @@
+-- An entity UUID identifies an entity across all webs, not only within its web.
+CREATE UNIQUE INDEX entity_ids_entity_uuid
+    ON entity_ids (entity_uuid);