diff --git a/token_bot/history_manager/history_manager.py b/token_bot/history_manager/history_manager.py
index 9501ae6..5226ce2 100644
--- a/token_bot/history_manager/history_manager.py
+++ b/token_bot/history_manager/history_manager.py
@@ -25,7 +25,7 @@ class HistoryManager:
         high_fidelity_history = await self._tdb.history(flavor, region, self.HIGH_FIDELITY_PERIOD)
         final_response = []
 
-        def _convert_to_datetime(data: Tuple[str, int]):
+        def _convert_to_datetime(data: Tuple[str, int]) -> Tuple[datetime.datetime, int]:
             return datetime.datetime.fromisoformat(data[0]), data[1]
 
         for data_point in all_history: