diff --git a/freqtrade/optimize/hyperopt.py b/freqtrade/optimize/hyperopt.py
index 534da34fc..4f8c0ea8b 100644
--- a/freqtrade/optimize/hyperopt.py
+++ b/freqtrade/optimize/hyperopt.py
@@ -270,7 +270,7 @@ class Hyperopt:
             self.backtesting.strategy.trailing_only_offset_is_reached = \
                 d['trailing_only_offset_is_reached']
 
-        processed = load(self.data_pickle_file)
+        processed = load(self.data_pickle_file, mmap_mode='r+')
 
         bt_results = self.backtesting.backtest(
             processed=processed,