diff --git a/freqtrade/exchange/exchange.py b/freqtrade/exchange/exchange.py
index 31ae20a1e..a06d328b3 100644
--- a/freqtrade/exchange/exchange.py
+++ b/freqtrade/exchange/exchange.py
@@ -139,7 +139,7 @@ class Exchange:
 
         # Holds candles
         self._klines: Dict[PairWithTimeframe, DataFrame] = {}
-        self._expiring_candle_cache: Dict[str, PeriodicCache] = {}
+        self._expiring_candle_cache: Dict[Tuple[str, int], PeriodicCache] = {}
 
         # Holds public_trades
         self._trades: Dict[PairWithTimeframe, DataFrame] = {}