diff -r 4a27b5ab2710 Lib/idlelib/IOBinding.py
--- a/Lib/idlelib/IOBinding.py	Wed Dec 14 18:40:35 2011 +0100
+++ b/Lib/idlelib/IOBinding.py	Wed Dec 14 12:37:48 2011 -0600
@@ -505,7 +505,8 @@
         dir, base = self.defaultfilename("save")
         if not self.savedialog:
             self.savedialog = tkFileDialog.SaveAs(master=self.text,
-                                                  filetypes=self.filetypes)
+                                                  filetypes=self.filetypes,
+                                                  defaultextension='')
         filename = self.savedialog.show(initialdir=dir, initialfile=base)
         return filename