diff -r f6a3310d3cc9 Lib/idlelib/EditorWindow.py
--- a/Lib/idlelib/EditorWindow.py	Sat Aug 01 11:07:11 2015 -0700
+++ b/Lib/idlelib/EditorWindow.py	Sun Aug 02 11:11:56 2015 +0530
@@ -351,18 +351,19 @@
 
     def _filename_to_unicode(self, filename):
         """convert filename to unicode in order to display it in Tk"""
-        if isinstance(filename, str) or not filename:
-            return filename
-        else:
+        #byte on decoding gives astral /non-BMP chars
+        if isinstance(filename, bytes):
             try:
-                return filename.decode(self.filesystemencoding)
+                filename = filename.decode(self.filesystemencoding)
             except UnicodeDecodeError:
                 # XXX
                 try:
-                    return filename.decode(self.encoding)
+                    filename = filename.decode(self.encoding)
                 except UnicodeDecodeError:
                     # byte-to-byte conversion
-                    return filename.decode('iso8859-1')
+                    filename = filename.decode('iso8859-1')
+        #replace non-BMP char with diamond questionmark.
+        return re.sub('[\U00010000-\U0010FFFF]', '\ufffd', filename)
 
     def new_callback(self, event):
         dirname, basename = self.io.defaultfilename()