diff --git a/src/app/db/migrations/0257_low_songbird.sql b/src/app/db/migrations/0257_low_songbird.sql
index 1647da23..18117e84 100644
--- a/src/app/db/migrations/0257_low_songbird.sql
+++ b/src/app/db/migrations/0257_low_songbird.sql
@@ -1,4 +1,4 @@
-CREATE INDEX CONCURRENTLY "ix_epc_building_part_epc_property" ON "epc_building_part" USING btree ("epc_property_id");--> statement-breakpoint
-CREATE INDEX CONCURRENTLY "ix_epc_energy_element_epc_property" ON "epc_energy_element" USING btree ("epc_property_id");--> statement-breakpoint
-CREATE INDEX CONCURRENTLY "ix_epc_floor_dimension_building_part" ON "epc_floor_dimension" USING btree ("epc_building_part_id");--> statement-breakpoint
-CREATE INDEX CONCURRENTLY "ix_property_portfolio" ON "property" USING btree ("portfolio_id");
\ No newline at end of file
+CREATE INDEX IF NOT EXISTS "ix_epc_building_part_epc_property" ON "epc_building_part" USING btree ("epc_property_id");--> statement-breakpoint
+CREATE INDEX IF NOT EXISTS "ix_epc_energy_element_epc_property" ON "epc_energy_element" USING btree ("epc_property_id");--> statement-breakpoint
+CREATE INDEX IF NOT EXISTS "ix_epc_floor_dimension_building_part" ON "epc_floor_dimension" USING btree ("epc_building_part_id");--> statement-breakpoint
+CREATE INDEX IF NOT EXISTS "ix_property_portfolio" ON "property" USING btree ("portfolio_id");
diff --git a/src/app/db/sql/prebuild-reporting-indexes.sql b/src/app/db/sql/prebuild-reporting-indexes.sql
new file mode 100644
index 00000000..2e6a9738
--- /dev/null
+++ b/src/app/db/sql/prebuild-reporting-indexes.sql
@@ -0,0 +1,21 @@
+-- Production pre-build for migration 0257 (reporting / EPC-graph FK indexes).
+--
+-- The drizzle migrator (src/app/db/migrate.ts) runs migrations inside a
+-- transaction, where CREATE INDEX CONCURRENTLY is not allowed. On a live,
+-- loaded database, run this file first via psql — it builds the same four
+-- indexes without blocking reads or writes — and 0257's
+-- CREATE INDEX IF NOT EXISTS then no-ops. On dev/CI databases the tables are
+-- small, so skipping this and letting 0257 build them directly is fine.
+--
+--   psql "$DATABASE_URL" -f src/app/db/sql/prebuild-reporting-indexes.sql
+--
+-- CONCURRENTLY waits out in-flight transactions between build phases, so
+-- long-running reporting queries can stall it — prefer a quiet window. If a
+-- build is interrupted it leaves an INVALID index (visible in \d+ <table>);
+-- DROP INDEX it and re-run. Note IF NOT EXISTS would also skip an INVALID
+-- leftover, so check before re-running.
+
+CREATE INDEX CONCURRENTLY IF NOT EXISTS "ix_epc_building_part_epc_property" ON "epc_building_part" USING btree ("epc_property_id");
+CREATE INDEX CONCURRENTLY IF NOT EXISTS "ix_epc_energy_element_epc_property" ON "epc_energy_element" USING btree ("epc_property_id");
+CREATE INDEX CONCURRENTLY IF NOT EXISTS "ix_epc_floor_dimension_building_part" ON "epc_floor_dimension" USING btree ("epc_building_part_id");
+CREATE INDEX CONCURRENTLY IF NOT EXISTS "ix_property_portfolio" ON "property" USING btree ("portfolio_id");