diff --git a/requirements-tests.txt b/requirements-tests.txt
index e079f8a..9299da7 100644
--- a/requirements-tests.txt
+++ b/requirements-tests.txt
@@ -1 +1,2 @@
 pytest
+pytz
diff --git a/src/solrq/__init__.py b/src/solrq/__init__.py
index 140e76b..e4b710e 100644
--- a/src/solrq/__init__.py
+++ b/src/solrq/__init__.py
@@ -65,7 +65,10 @@ def __init__(self, raw, safe=False):
         if isinstance(raw, datetime) and not safe:
             # Note: solr speaks ISO, wrap it with quotes to avoid further
             # escaping
-            self.raw = '"{dt}"'.format(dt=raw.isoformat())
+            self.raw = '"{dt}Z"'.format(
+                dt=(raw.strftime('%Y-%m-%dT%H:%M:%S.%f') if raw.tzinfo
+                    else raw.isoformat())
+            )
             # since we translated value we can safely mark it safe
             self.safe = True
         elif isinstance(raw, timedelta) and not safe:
diff --git a/tests/test_squery.py b/tests/test_squery.py
index 596f259..fba4c69 100644
--- a/tests/test_squery.py
+++ b/tests/test_squery.py
@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 import pytest
 from datetime import datetime, timedelta
+import pytz
 
 from solrq import (
     Q, QOperator, Value, Range, Proximity, ANY, SET
@@ -102,9 +103,18 @@ def test_value():
     assert str(Value('"foo bar"', safe=True), ) == '"foo bar"'
 
 
-def test_value_datetimes():
+def test_value_nonlocalized_datetimes():
     dt = datetime.now()
-    assert str(Value(dt)) == '"{dt}"'.format(dt=dt.isoformat())
+    assert str(Value(dt)) == '"{dt}Z"'.format(dt=dt.isoformat())
+
+
+def test_value_localized_datetimes():
+    dt = datetime.now()
+    dt = dt.replace(tzinfo=pytz.timezone('Europe/Warsaw'))
+
+    assert str(Value(dt)) == '"{dt}Z"'.format(
+        dt=dt.strftime('%Y-%m-%dT%H:%M:%S.%f')
+    )
 
 
 def test_value_timedelta():
diff --git a/tox.ini b/tox.ini
index 0be2a0e..13609df 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,7 +9,6 @@ setenv = VIRTUAL_ENV = {envdir}
 # but they are not run later in coverage because they are only illustratory
 commands = py.test --doctest-modules --ignore=setup.py --ignore docs {posargs}
 sitepackages = False
-downloadcache = {toxworkdir}/_download
 
 [testenv:pep8]
 deps = flake8==2.0