diff --git a/backend/app/tasks/translate_and_synthesize.py b/backend/app/tasks/translate_and_synthesize.py
index 98c083d..5d2ab7a 100644
--- a/backend/app/tasks/translate_and_synthesize.py
+++ b/backend/app/tasks/translate_and_synthesize.py
@@ -280,14 +280,21 @@ async def _async_translate_and_synthesize(job_id: str, languages: list[str] | No
         finally:
             pass
 
-        # Update status to TTS generating
+        # Update status to TTS generating.
+        # Use per-language dot-notation so concurrent single-language retranslation tasks
+        # don't overwrite each other's results (concurrency:2 race condition).
+        per_lang_updates = {
+            f"outputs.{lang}": updated_outputs[lang]
+            for lang in target_languages
+            if lang in updated_outputs
+        }
         await db.jobs.update_one(
             {"_id": job_id},
             {
                 "$set": {
                     "status": JobStatus.TTS_GENERATING.value,
-                    "outputs": updated_outputs,
-                    "updated_at": datetime.utcnow()
+                    "updated_at": datetime.utcnow(),
+                    **per_lang_updates,
                 },
                 "$push": {
                     "review.history": {