diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
index a346b67de4ce..503c0b76254a 100644
--- a/lib/matplotlib/backend_bases.py
+++ b/lib/matplotlib/backend_bases.py
@@ -1974,6 +1974,7 @@ def idle_event(self, guiEvent=None):
         s = 'idle_event'
         event = IdleEvent(s, self, guiEvent=guiEvent)
         self.callbacks.process(s, event)
+        return True
 
     def grab_mouse(self, ax):
         """