diff --git a/services/processor/src/schema-guard.service.ts b/services/processor/src/schema-guard.service.ts
index b560d9c..d0f431d 100644
--- a/services/processor/src/schema-guard.service.ts
+++ b/services/processor/src/schema-guard.service.ts
@@ -28,6 +28,17 @@ export class SchemaGuardService implements OnModuleInit {
   constructor(@InjectDataSource() private readonly dataSource: DataSource) {}
 
   async onModuleInit(): Promise<void> {
+    // Pre-dedupe: legacy rows without the index can block CREATE UNIQUE INDEX.
+    await this.dataSource.query(`
+      DELETE FROM aggregated_metrics a
+      USING aggregated_metrics b
+      WHERE a.ctid < b.ctid
+        AND a."metricType" = b."metricType"
+        AND a."granularity" = b."granularity"
+        AND a."timestamp" = b."timestamp"
+        AND a."dimension" IS NOT DISTINCT FROM b."dimension"
+        AND a."dimensionValue" IS NOT DISTINCT FROM b."dimensionValue"
+    `);
     await this.dataSource.query(`
       CREATE UNIQUE INDEX IF NOT EXISTS uq_aggregated_metrics_dedup
       ON aggregated_metrics ("metricType", "granularity", "timestamp", "dimension", "dimensionValue")