diff --git a/great_ai/persistence/parallel_tinydb_driver.py b/great_ai/persistence/parallel_tinydb_driver.py
index 8a2896f..bf186c5 100644
--- a/great_ai/persistence/parallel_tinydb_driver.py
+++ b/great_ai/persistence/parallel_tinydb_driver.py
@@ -28,10 +28,10 @@ class ParallelTinyDbDriver(TracingDatabaseDriver):
     path_to_db = Path(DEFAULT_TRACING_DB_FILENAME)
 
     def save(self, trace: Trace) -> str:
-        return self._safe_execute(lambda db: db.insert(trace.model_dump()))
+        return self._safe_execute(lambda db: db.insert(trace.model_dump(mode="json")))
 
     def save_batch(self, documents: List[Trace]) -> List[str]:
-        traces = [d.model_dump() for d in documents]
+        traces = [d.model_dump(mode="json") for d in documents]
         return self._safe_execute(lambda db: db.insert_multiple(traces))
 
     def get(self, id: str) -> Optional[Trace]:
@@ -100,7 +100,7 @@ class ParallelTinyDbDriver(TracingDatabaseDriver):
     def update(self, id: str, new_version: Trace) -> None:
         self._safe_execute(
             lambda db: db.update(
-                new_version.model_dump(), lambda d: d["trace_id"] == id
+                new_version.model_dump(mode="json"), lambda d: d["trace_id"] == id
             )
         )
 
diff --git a/tests/test_persistence_serialization.py b/tests/test_persistence_serialization.py
new file mode 100644
index 0000000..aa24cc0
--- /dev/null
+++ b/tests/test_persistence_serialization.py
@@ -0,0 +1,36 @@
+from datetime import datetime, timezone
+from typing import Set
+
+from fastapi.testclient import TestClient
+from great_ai import GreatAI
+from great_ai.context import get_context
+from pydantic import BaseModel
+
+
+class DatedInput(BaseModel):
+    when: datetime
+    tags: Set[int]
+
+
+def test_tinydb_persists_json_compatible_model_values(isolated_context: None) -> None:
+    @GreatAI.create
+    def predict(data: DatedInput) -> int:
+        return len(data.tags)
+
+    with TestClient(predict.app) as client:
+        response = client.post(
+            "/predict", json={"data": {"when": "2026-01-01T00:00:00Z", "tags": [1, 2]}}
+        )
+        assert response.status_code == 200
+        trace_id = response.json()["trace_id"]
+    database = get_context().tracing_database
+    trace = database.get(trace_id)
+    assert trace is not None
+    assert trace.output == 2
+    trace.feedback = {"when": datetime(2026, 1, 1, tzinfo=timezone.utc)}
+    database.update(trace_id, trace)
+    updated = database.get(trace_id)
+    assert updated is not None
+    assert updated.feedback == {"when": "2026-01-01T00:00:00Z"}
+    database.save_batch([trace.model_copy(update={"trace_id": "batch"})])
+    assert database.get("batch") is not None