diff --git a/acme/acme/jose/interfaces.py b/acme/acme/jose/interfaces.py
index f85777a30..f841848b3 100644
--- a/acme/acme/jose/interfaces.py
+++ b/acme/acme/jose/interfaces.py
@@ -194,7 +194,7 @@ class JSONDeSerializable(object):
         :rtype: str
 
         """
-        return self.json_dumps(sort_keys=True, indent=4)
+        return self.json_dumps(sort_keys=True, indent=4, separators=(',', ': '))
 
     @classmethod
     def json_dump_default(cls, python_object):
diff --git a/acme/acme/jose/interfaces_test.py b/acme/acme/jose/interfaces_test.py
index 84dc2a1be..cf98ff371 100644
--- a/acme/acme/jose/interfaces_test.py
+++ b/acme/acme/jose/interfaces_test.py
@@ -1,8 +1,6 @@
 """Tests for acme.jose.interfaces."""
 import unittest
 
-import six
-
 
 class JSONDeSerializableTest(unittest.TestCase):
     # pylint: disable=too-many-instance-attributes
@@ -92,9 +90,8 @@ class JSONDeSerializableTest(unittest.TestCase):
         self.assertEqual('["foo1", "foo2"]', self.seq.json_dumps())
 
     def test_json_dumps_pretty(self):
-        filler = ' ' if six.PY2 else ''
         self.assertEqual(self.seq.json_dumps_pretty(),
-                         '[\n    "foo1",{0}\n    "foo2"\n]'.format(filler))
+                         '[\n    "foo1",\n    "foo2"\n]')
 
     def test_json_dump_default(self):
         from acme.jose.interfaces import JSONDeSerializable