diff --git a/freqtrade/data/history/jsondatahandler.py b/freqtrade/data/history/jsondatahandler.py
index 990e75bd9..24d6e814b 100644
--- a/freqtrade/data/history/jsondatahandler.py
+++ b/freqtrade/data/history/jsondatahandler.py
@@ -62,7 +62,7 @@ class JsonDataHandler(IDataHandler):
         filename = self._pair_data_filename(self._datadir, pair, timeframe)
         _data = data.copy()
         # Convert date to int
-        _data['date'] = _data['date'].astype(np.int64) // 1000 // 1000
+        _data['date'] = _data['date'].view(np.int64) // 1000 // 1000
 
         # Reset index, select only appropriate columns and save as json
         _data.reset_index(drop=True).loc[:, self._columns].to_json(