diff --git a/cola/core/mq/store.py b/cola/core/mq/store.py
index 1087147..d7b5f5d 100755
--- a/cola/core/mq/store.py
+++ b/cola/core/mq/store.py
@@ -254,7 +254,8 @@ def put_one(self, obj, force=False, commit=True):
             if self.deduper.exist(prop):
                 return
         if len(self.legal_files) == 0:
-            self._generate_file()
+            with self.lock:
+                self._generate_file()
             
         obj_str = self._stringfy(obj)
         # If no file has enough space