diff --git a/Lib/idlelib/IOBinding.py b/Lib/idlelib/IOBinding.py
index 9528c9a..ec50eb2 100644
--- a/Lib/idlelib/IOBinding.py
+++ b/Lib/idlelib/IOBinding.py
@@ -485,6 +485,8 @@
         ("All files", "*"),
         ]
 
+    defaultextension = '.py' if sys.platform == 'darwin' else ''
+
     def askopenfile(self):
         dir, base = self.defaultfilename("open")
         if not self.opendialog:
@@ -508,8 +510,10 @@
     def asksavefile(self):
         dir, base = self.defaultfilename("save")
         if not self.savedialog:
-            self.savedialog = tkFileDialog.SaveAs(master=self.text,
-                                                  filetypes=self.filetypes)
+            self.savedialog = tkFileDialog.SaveAs(
+                    master=self.text,
+                    filetypes=self.filetypes,
+                    defaultextension=self.defaultextension)
         filename = self.savedialog.show(initialdir=dir, initialfile=base)
         return filename
 
diff --git a/Lib/idlelib/NEWS.txt b/Lib/idlelib/NEWS.txt
index e2f31c3..0cdf7a6 100644
--- a/Lib/idlelib/NEWS.txt
+++ b/Lib/idlelib/NEWS.txt
@@ -1,6 +1,9 @@
 What's New in IDLE 3.3.0?
 =========================
 
+- Issue #4832: Modify IDLE to save files with .py extension by
+  default on Windows and OS X (Tk 8.5) as it already does with X11 Tk.
+
 - Issue #13532, #15319: Check that arguments to sys.stdout.write are strings.
 
 - Issue # 12510: Attempt to get certain tool tips no longer crashes IDLE.