diff --git a/IPython/core/history.py b/IPython/core/history.py
index da10813..c9b8435 100644
--- a/IPython/core/history.py
+++ b/IPython/core/history.py
@@ -775,6 +775,7 @@ class HistorySavingThread(threading.Thread):
             while True:
                 self.history_manager.save_flag.wait()
                 if self.stop_now:
+                    self.db.close()
                     return
                 self.history_manager.save_flag.clear()
                 self.history_manager.writeout_cache(self.db)