diff -r 6d2982ff441f Lib/idlelib/keybindingDialog.py
--- a/Lib/idlelib/keybindingDialog.py	Thu May 15 20:50:10 2014 -0400
+++ b/Lib/idlelib/keybindingDialog.py	Sun May 18 11:20:50 2014 +0530
@@ -234,6 +234,9 @@
         keySequence = keys.split()
         keysOK = False
         title = 'Key Sequence Error'
+        # flatten to a one dimension list for overlap check:
+        currentKeySequences = [[i]
+                            for key in self.currentKeySequences for i in key]
         if not keys:
             tkMessageBox.showerror(title=title, parent=self,
                                    message='No keys specified.')
@@ -250,7 +253,7 @@
             msg = 'The shift modifier by itself may not be used with'\
                   ' this key symbol.'
             tkMessageBox.showerror(title=title, parent=self, message=msg)
-        elif keySequence in self.currentKeySequences:
+        elif keySequence in currentKeySequences:
             msg = 'This key combination is already in use.'
             tkMessageBox.showerror(title=title, parent=self, message=msg)
         else: