diff --git a/mtda/storage/writer.py b/mtda/storage/writer.py
index 332110ba..520360d1 100644
--- a/mtda/storage/writer.py
+++ b/mtda/storage/writer.py
@@ -93,8 +93,9 @@ def flush(self, size):
         self._receiving = False
         self._size = size
 
-        self.mtda.debug(2, "storage.writer.flush(): waiting on thread...")
-        self._thread.join()
+        if self._thread is not None:
+            self.mtda.debug(2, "storage.writer.flush(): waiting on thread...")
+            self._thread.join()
         result = not self._failed
 
         self.mtda.debug(3, f"storage.writer.flush(): {result}")