diff --git a/freqtrade/freqtradebot.py b/freqtrade/freqtradebot.py
index 32adc6d57..163c4faaa 100644
--- a/freqtrade/freqtradebot.py
+++ b/freqtrade/freqtradebot.py
@@ -1172,7 +1172,7 @@ class FreqtradeBot:
         if order_amount is None:
             order_amount = order['amount']
         # Only run for closed orders
-        if trade.fee_updated(order.get('side')) or order['status'] == 'open':
+        if trade.fee_updated(order.get('side', '')) or order['status'] == 'open':
             return order_amount
 
         trade_base_currency = self.exchange.get_pair_base_currency(trade.pair)
@@ -1185,7 +1185,7 @@ class FreqtradeBot:
                 order_amount = order_amount - fee_cost
                 logger.info(f"Applying fee on amount for {trade} (from {order['amount']} "
                             f"to {order_amount}) from Order")
-            trade.update_fee(fee_cost, fee_currency, fee_rate, order.get('side'))
+            trade.update_fee(fee_cost, fee_currency, fee_rate, order.get('side', ''))
             return order_amount
         return self.fee_detection_from_trades(trade, order, order_amount)
 
@@ -1220,7 +1220,7 @@ class FreqtradeBot:
             # fee_rate should use mean
 
             fee_rate = sum(fee_rate_array) / float(len(fee_rate_array)) if fee_rate_array else None
-            trade.update_fee(fee_cost, fee_currency, fee_rate, order.get('side'))
+            trade.update_fee(fee_cost, fee_currency, fee_rate, order.get('side', ''))
 
         if not isclose(amount, order_amount, abs_tol=constants.MATH_CLOSE_PREC):
             logger.warning(f"Amount {amount} does not match amount {trade.amount}")
diff --git a/freqtrade/persistence.py b/freqtrade/persistence.py
index 17246633c..ea34fd5bf 100644
--- a/freqtrade/persistence.py
+++ b/freqtrade/persistence.py
@@ -377,7 +377,7 @@ class Trade(_DECL_BASE):
         )
 
     def update_fee(self, fee_cost: float, fee_currency: Optional[str], fee_rate: Optional[float],
-                   side) -> None:
+                   side: str) -> None:
         """
         Update Fee parameters. Only acts once per side
         """
@@ -394,7 +394,7 @@ class Trade(_DECL_BASE):
             if fee_rate is not None:
                 self.fee_close = fee_rate
 
-    def fee_updated(self, side) -> bool:
+    def fee_updated(self, side: str) -> bool:
         """
         Verify if this side (buy / sell) has already been updated
         """