diff -r 55d50b544a3d Lib/idlelib/PyShell.py
--- a/Lib/idlelib/PyShell.py	Sun Oct 12 09:53:12 2014 +0200
+++ b/Lib/idlelib/PyShell.py	Sun Oct 12 13:32:30 2014 +0300
@@ -151,6 +151,9 @@ class PyShellEditorWindow(EditorWindow):
 
     def color_breakpoint_text(self, color=True):
         "Turn colorizing of breakpoint text on or off"
+        if self.io is None:
+            # can happen if IDLE closes due to the .update() call
+            return
         if color:
             theme = idleConf.GetOption('main','Theme','name')
             cfg = idleConf.GetHighlight(theme, "break")