diff --git a/moss_transcribe_diarize/app/jobs.py b/moss_transcribe_diarize/app/jobs.py
index ef977fb..ee3ce5e 100644
--- a/moss_transcribe_diarize/app/jobs.py
+++ b/moss_transcribe_diarize/app/jobs.py
@@ -316,9 +316,10 @@ def render(self, job_id: str, style_payload: dict[str, Any] | None = None) -> Jo
             raise RuntimeError("ffmpeg and ffprobe are not available on PATH.")
         if not job.segments_path.exists():
             raise RuntimeError("No subtitle segments are available for this job.")
+        resolved_style = job.subtitle_style if style_payload is None else style_payload
         threading.Thread(
             target=self._render_job,
-            args=(job.id, SubtitleStyle.from_dict(style_payload)),
+            args=(job.id, SubtitleStyle.from_dict(resolved_style)),
             name=f"mtd-render-{job.id}",
             daemon=True,
         ).start()
diff --git a/tests/test_app_api.py b/tests/test_app_api.py
index 7db6610..0778c47 100644
--- a/tests/test_app_api.py
+++ b/tests/test_app_api.py
@@ -213,6 +213,73 @@ def test_running_job_exposes_live_token_progress(self):
             self.assertEqual(finished["status"], "waiting_review")
             self.assertEqual(finished["usage"]["generated_tokens"], 5)
 
+    def test_render_reuses_saved_style_unless_explicitly_overridden(self):
+        from fastapi.testclient import TestClient
+        from moss_transcribe_diarize.app.server import create_app
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            app = create_app(model_path="fake-model", runs_dir=tmpdir)
+            app.state.manager.model_runner = FakeRunner()
+            client = TestClient(app)
+
+            created = client.post(
+                "/api/jobs",
+                files={"file": ("sample.wav", b"audio", "audio/wav")},
+            )
+            self.assertEqual(created.status_code, 200)
+            job_id = created.json()["id"]
+
+            job = {}
+            for _ in range(40):
+                job = client.get(f"/api/jobs/{job_id}").json()
+                if job["status"] == "waiting_review":
+                    break
+                time.sleep(0.05)
+            self.assertEqual(job["status"], "waiting_review")
+
+            segments = client.get(f"/api/jobs/{job_id}/segments").json()["segments"]
+            updated = client.put(
+                f"/api/jobs/{job_id}/segments",
+                json={
+                    "segments": segments,
+                    "style": {
+                        "font_size": 42,
+                        "margin_v": 80,
+                        "speaker_names": {"S01": "Alice"},
+                    },
+                },
+            )
+            self.assertEqual(updated.status_code, 200)
+
+            class Available:
+                available = True
+
+            with patch("moss_transcribe_diarize.app.jobs.detect_ffmpeg", return_value=Available()), patch(
+                "moss_transcribe_diarize.app.jobs.threading.Thread"
+            ) as thread_cls:
+                rendered = client.post(f"/api/jobs/{job_id}/render")
+                self.assertEqual(rendered.status_code, 200)
+                saved_style = thread_cls.call_args.kwargs["args"][1]
+                self.assertEqual(saved_style.font_size, 42)
+                self.assertEqual(saved_style.margin_v, 80)
+                self.assertEqual(saved_style.speaker_names, {"S01": "Alice"})
+
+                overridden = client.post(
+                    f"/api/jobs/{job_id}/render",
+                    json={
+                        "style": {
+                            "font_size": 60,
+                            "margin_v": 96,
+                            "speaker_names": {"S01": "Bob"},
+                        }
+                    },
+                )
+                self.assertEqual(overridden.status_code, 200)
+                explicit_style = thread_cls.call_args.kwargs["args"][1]
+                self.assertEqual(explicit_style.font_size, 60)
+                self.assertEqual(explicit_style.margin_v, 96)
+                self.assertEqual(explicit_style.speaker_names, {"S01": "Bob"})
+
 
 if __name__ == "__main__":
     unittest.main()