diff -r f0202c3daa7a Lib/json/encoder.py
--- a/Lib/json/encoder.py	Fri Aug 23 03:22:15 2013 -0500
+++ b/Lib/json/encoder.py	Fri Aug 23 14:55:28 2013 +0400
@@ -322,6 +322,30 @@
         if markers is not None:
             del markers[markerid]
 
+    def _encode_dict_key(key, recursed=False):
+        if isinstance(key, str):
+            pass
+        # JavaScript is weakly typed for these, so it makes sense to
+        # also allow them.  Many encoders seem to do something like this.
+        elif isinstance(key, float):
+            # see comment for int/float in _make_iterencode
+            key = _floatstr(float(key))
+        elif key is True:
+            key = 'true'
+        elif key is False:
+            key = 'false'
+        elif key is None:
+            key = 'null'
+        elif isinstance(key, int):
+            # see comment for int/float in _make_iterencode
+            key = str(int(key))
+        elif not recursed:
+            key = _default(key)
+            key = _encode_dict_key(key, recursed=True)
+        else:
+            raise TypeError("key " + repr(key) + " is not a string")
+        return key
+
     def _iterencode_dict(dct, _current_indent_level):
         if not dct:
             yield '{}'
@@ -346,26 +370,13 @@
         else:
             items = dct.items()
         for key, value in items:
-            if isinstance(key, str):
-                pass
-            # JavaScript is weakly typed for these, so it makes sense to
-            # also allow them.  Many encoders seem to do something like this.
-            elif isinstance(key, float):
-                # see comment for int/float in _make_iterencode
-                key = _floatstr(float(key))
-            elif key is True:
-                key = 'true'
-            elif key is False:
-                key = 'false'
-            elif key is None:
-                key = 'null'
-            elif isinstance(key, int):
-                # see comment for int/float in _make_iterencode
-                key = str(int(key))
-            elif _skipkeys:
-                continue
-            else:
-                raise TypeError("key " + repr(key) + " is not a string")
+            try:
+                key = _encode_dict_key(key)
+            except TypeError:
+                if _skipkeys:
+                    continue
+                else:
+                    raise
             if first:
                 first = False
             else: