diff --git a/freqtrade/data/datahandlers/jsondatahandler.py b/freqtrade/data/datahandlers/jsondatahandler.py
index a6caf137d..747d80c54 100644
--- a/freqtrade/data/datahandlers/jsondatahandler.py
+++ b/freqtrade/data/datahandlers/jsondatahandler.py
@@ -25,13 +25,13 @@ class JsonDataHandler(IDataHandler):
         # Check if regex found something and only return these results
         return [match[0].replace('_', '/') for match in _tmp if match]
 
-    def ohlcv_store(self, timeframe: str, data: DataFrame):
+    def ohlcv_store(self, timeframe: str, data: DataFrame) -> None:
         """
         Store data
         """
         raise NotImplementedError()
 
-    def ohlcv_append(self, timeframe: str, data: DataFrame):
+    def ohlcv_append(self, timeframe: str, data: DataFrame) -> None:
         """
         Append data to existing files
         """
diff --git a/freqtrade/utils.py b/freqtrade/utils.py
index 0805f0011..72b2afc8e 100644
--- a/freqtrade/utils.py
+++ b/freqtrade/utils.py
@@ -286,9 +286,9 @@ def convert_ohlcv_format(config: Dict[str, Any], convert_from: str, convert_to:
         for pair in config['pairs']:
             src = SrcClass(Path(config['datadir']), pair)
             trg = TrgClass(Path(config['datadir']), pair)
-            data = src.ohlcv_load(timeframe)
+            data = src.ohlcv_load(timeframe=timeframe)
             logger.info(f"Converting {len(data)} candles for {pair}")
-        #     trg.ohlcv_store(data)
+            trg.ohlcv_store(timeframe=timeframe, data=data)
 
 
 def start_convert_data(args: Dict[str, Any], ohlcv: bool = True) -> None: