diff --git a/src/dexorder/final_ohlc.py b/src/dexorder/final_ohlc.py
index c88c83f..bd4d9ef 100644
--- a/src/dexorder/final_ohlc.py
+++ b/src/dexorder/final_ohlc.py
@@ -214,7 +214,7 @@ class OHLCFileSeries:
         self.base_dir = base_dir
         self.symbol = symbol
         self.series_start: Optional[datetime] = None  # timestamp of the first datum in the series
-        self.write_offset: Optional[int] = None
+        self.write_offset: int = 0
         self.last_flush: Optional[tuple[datetime,dec]] = None
         self.quote_file = None
         self.dirty_files = set()