diff -r 0ca9e0aa06df Lib/idlelib/IOBinding.py
--- a/Lib/idlelib/IOBinding.py	Fri Jul 25 00:55:23 2014 +0200
+++ b/Lib/idlelib/IOBinding.py	Fri Jul 25 11:04:08 2014 +0800
@@ -233,8 +233,34 @@
             chars = self.eol_re.sub(r"\n", chars)
         self.text.delete("1.0", "end")
         self.set_filename(None)
-        self.text.insert("1.0", chars)
         self.reset_undo()
+        
+        try:
+            self.text.insert("1.0", chars)
+        except:
+            # check non-bmp character
+            line_count = 1
+            position_count = 0
+            for char in chars:
+                if char == '\n':
+                    line_count += 1
+                    position_count = 0
+                elif ord(char) > 0xFFFF:
+                    nonbmp_msg = \
+                        ("IDLE can't display non-BMP characters "
+                         "(codepoint above 0xFFFF).\n"
+                         "A non-BMP character (codepoint 0x%X) "
+                         "found at line %d, position %d of file %s.\n\n"
+                         "Please open this file with another editor.")
+                    tkMessageBox.showerror("non-BMP character",
+                                           nonbmp_msg %
+                                           (ord(char), line_count,
+                                            position_count, filename),
+                                           parent=self.text)
+                    return False
+                position_count += 1
+            raise
+        
         self.set_filename(filename)
         if converted:
             # We need to save the conversion results first