diff --git a/overviewer_core/progressbar.py b/overviewer_core/progressbar.py
index a2a54aa..9b743d0 100644
--- a/overviewer_core/progressbar.py
+++ b/overviewer_core/progressbar.py
@@ -314,6 +314,7 @@ class ProgressBar(object):
         else:
             self.finished = True
             self.fd.write(self._format_line() + '\n')
+        self.fd.flush()
         return True
 
     def start(self):