diff --git a/services/mam-api/src/db/schema_patch_editor.sql b/services/mam-api/src/db/schema_patch_editor.sql
index 476daf6..1080703 100644
--- a/services/mam-api/src/db/schema_patch_editor.sql
+++ b/services/mam-api/src/db/schema_patch_editor.sql
@@ -43,19 +43,44 @@ CREATE INDEX IF NOT EXISTS idx_sequence_clips_asset_id       ON sequence_clips(a
 -- ---------------------------------------------------------------------------
 -- Idempotent ALTER TABLE block — applies the new constraints and index to
 -- tables that were already created by an earlier run of this file.
--- Safe to re-run: ADD CONSTRAINT IF NOT EXISTS / CREATE INDEX IF NOT EXISTS.
+-- Uses DO blocks because PostgreSQL does not support ADD CONSTRAINT IF NOT EXISTS.
+-- Safe to re-run.
 -- ---------------------------------------------------------------------------
 
-ALTER TABLE sequences
-  ADD CONSTRAINT IF NOT EXISTS uq_sequences_project_name UNIQUE (project_id, name);
+DO $$ BEGIN
+  IF NOT EXISTS (
+    SELECT 1 FROM pg_constraint
+    WHERE conname = 'uq_sequences_project_name' AND conrelid = 'sequences'::regclass
+  ) THEN
+    ALTER TABLE sequences ADD CONSTRAINT uq_sequences_project_name UNIQUE (project_id, name);
+  END IF;
+END $$;
 
-ALTER TABLE sequence_clips
-  ADD CONSTRAINT IF NOT EXISTS chk_timeline_range CHECK (timeline_out_frames > timeline_in_frames);
+DO $$ BEGIN
+  IF NOT EXISTS (
+    SELECT 1 FROM pg_constraint
+    WHERE conname = 'chk_timeline_range' AND conrelid = 'sequence_clips'::regclass
+  ) THEN
+    ALTER TABLE sequence_clips ADD CONSTRAINT chk_timeline_range CHECK (timeline_out_frames > timeline_in_frames);
+  END IF;
+END $$;
 
-ALTER TABLE sequence_clips
-  ADD CONSTRAINT IF NOT EXISTS chk_source_range CHECK (source_out_frames > source_in_frames);
+DO $$ BEGIN
+  IF NOT EXISTS (
+    SELECT 1 FROM pg_constraint
+    WHERE conname = 'chk_source_range' AND conrelid = 'sequence_clips'::regclass
+  ) THEN
+    ALTER TABLE sequence_clips ADD CONSTRAINT chk_source_range CHECK (source_out_frames > source_in_frames);
+  END IF;
+END $$;
 
-ALTER TABLE sequence_clips
-  ADD CONSTRAINT IF NOT EXISTS chk_track_valid CHECK (track >= 0);
+DO $$ BEGIN
+  IF NOT EXISTS (
+    SELECT 1 FROM pg_constraint
+    WHERE conname = 'chk_track_valid' AND conrelid = 'sequence_clips'::regclass
+  ) THEN
+    ALTER TABLE sequence_clips ADD CONSTRAINT chk_track_valid CHECK (track >= 0);
+  END IF;
+END $$;
 
 CREATE INDEX IF NOT EXISTS idx_sequence_clips_asset_id ON sequence_clips(asset_id);