Index: Lib/json/tests/test_indent.py
===================================================================
--- Lib/json/tests/test_indent.py	(revision 84213)
+++ Lib/json/tests/test_indent.py	(working copy)
@@ -2,6 +2,7 @@
 
 import json
 import textwrap
+from StringIO import StringIO
 
 class TestIndent(TestCase):
     def test_indent(self):
@@ -39,3 +40,19 @@
         self.assertEquals(h1, h)
         self.assertEquals(h2, h)
         self.assertEquals(d2, expect)
+
+    def test_indent0(self):
+        h = {3: 1, 4: 2}
+
+        def check(indent, expected):
+            d1 = json.dumps(h, indent=indent)
+            self.assertEquals(d1, expected)
+
+            sio = StringIO()
+            json.dump({3: 1, 4: 2}, sio, indent=indent)
+            self.assertEquals(sio.getvalue(), expected)
+
+        # indent=0 should emit newlines
+        check(0, '{\n"3": 1, \n"4": 2\n}')
+        # indent=None is more compact
+        check(None, '{"3": 1, "4": 2}')
Index: Lib/json/encoder.py
===================================================================
--- Lib/json/encoder.py	(revision 84213)
+++ Lib/json/encoder.py	(working copy)
@@ -251,7 +251,7 @@
 
 
         if (_one_shot and c_make_encoder is not None
-                and not self.indent and not self.sort_keys):
+                and self.indent is None and not self.sort_keys):
             _iterencode = c_make_encoder(
                 markers, self.default, _encoder, self.indent,
                 self.key_separator, self.item_separator, self.sort_keys,