diff --git a/backend/src/main/resources/db/migration/V36__add_index_transcription_blocks_document_id.sql b/backend/src/main/resources/db/migration/V36__add_index_transcription_blocks_document_id.sql
new file mode 100644
index 00000000..2c109324
--- /dev/null
+++ b/backend/src/main/resources/db/migration/V36__add_index_transcription_blocks_document_id.sql
@@ -0,0 +1,4 @@
+-- Index on transcription_blocks.document_id to speed up the LATERAL join
+-- used in DocumentService.findEnrichmentData (FTS match enrichment).
+CREATE INDEX IF NOT EXISTS idx_transcription_blocks_document_id
+    ON transcription_blocks (document_id);