diff --git a/letsencrypt/acme/fields.py b/letsencrypt/acme/fields.py
index 59a72953b..f001f1cd5 100644
--- a/letsencrypt/acme/fields.py
+++ b/letsencrypt/acme/fields.py
@@ -5,7 +5,13 @@ from letsencrypt.acme import jose
 
 
 class RFC3339Field(jose.Field):
-    """RFC3339 field encoder/decoder"""
+    """RFC3339 field encoder/decoder.
+
+    Handles decoding/encoding between RFC3339 strings and aware (not
+    naive) `datetime.datetime` objects
+    (e.g. ``datetime.datetime.now(pytz.utc)``).
+
+    """
 
     @classmethod
     def default_encoder(cls, value):
diff --git a/letsencrypt/acme/fields_test.py b/letsencrypt/acme/fields_test.py
new file mode 100644
index 000000000..204849408
--- /dev/null
+++ b/letsencrypt/acme/fields_test.py
@@ -0,0 +1,35 @@
+"""Tests for letsencrypt.acme.fields."""
+import datetime
+import unittest
+
+import pytz
+
+from letsencrypt.acme import jose
+
+
+class RFC3339FieldTest(unittest.TestCase):
+    """Tests for letsencrypt.acme.fields.RFC3339Field."""
+
+    def setUp(self):
+        self.decoded = datetime.datetime(2015, 3, 27, tzinfo=pytz.utc)
+        self.encoded = '2015-03-27T00:00:00Z'
+
+    def test_default_encoder(self):
+        from letsencrypt.acme.fields import RFC3339Field
+        self.assertEqual(
+            self.encoded, RFC3339Field.default_encoder(self.decoded))
+
+    def test_default_encoder_naive_fails(self):
+        from letsencrypt.acme.fields import RFC3339Field
+        self.assertRaises(
+            ValueError, RFC3339Field.default_encoder, datetime.datetime.now())
+
+    def test_default_decoder(self):
+        from letsencrypt.acme.fields import RFC3339Field
+        self.assertEqual(
+            self.decoded, RFC3339Field.default_decoder(self.encoded))
+
+    def test_default_decoder_raises_deserialization_error(self):
+        from letsencrypt.acme.fields import RFC3339Field
+        self.assertRaises(
+            jose.DeserializationError, RFC3339Field.default_decoder, '')
diff --git a/setup.py b/setup.py
index b25b7fdb4..b70bfa031 100644
--- a/setup.py
+++ b/setup.py
@@ -39,6 +39,7 @@ install_requires = [
     'pyrfc3339',
     'python-augeas',
     'python2-pythondialog',
+    'pytz',
     'requests',
     'werkzeug',
     'zope.component',