diff --git a/django/utils/cache.py b/django/utils/cache.py
index 1015c2f277..0ea84072fa 100644
--- a/django/utils/cache.py
+++ b/django/utils/cache.py
@@ -165,7 +165,9 @@ def _i18n_cache_key_suffix(request, cache_key):
         # which in turn can also fall back to settings.LANGUAGE_CODE
         cache_key += '.%s' % getattr(request, 'LANGUAGE_CODE', get_language())
     if settings.USE_TZ:
-        cache_key += '.%s' % get_current_timezone_name()
+        # Windows uses non-standard timezone names that may include spaces,
+        # which triggers CacheKeyWarning.
+        cache_key += '.%s' % get_current_timezone_name().replace(' ', '_')
     return cache_key
 
 def _generate_cache_key(request, method, headerlist, key_prefix):
diff --git a/tests/regressiontests/cache/tests.py b/tests/regressiontests/cache/tests.py
index 779e3fedf8..8faaa6fdc4 100644
--- a/tests/regressiontests/cache/tests.py
+++ b/tests/regressiontests/cache/tests.py
@@ -1270,7 +1270,7 @@ class CacheI18nTest(TestCase):
     @override_settings(USE_I18N=False, USE_L10N=False, USE_TZ=True)
     def test_cache_key_i18n_timezone(self):
         request = self._get_request()
-        tz = timezone.get_current_timezone_name()
+        tz = timezone.get_current_timezone_name().replace(' ', '_')
         response = HttpResponse()
         key = learn_cache_key(request, response)
         self.assertIn(tz, key, "Cache keys should include the time zone name when time zones are active")
@@ -1281,7 +1281,7 @@ class CacheI18nTest(TestCase):
     def test_cache_key_no_i18n (self):
         request = self._get_request()
         lang = translation.get_language()
-        tz = timezone.get_current_timezone_name()
+        tz = timezone.get_current_timezone_name().replace(' ', '_')
         response = HttpResponse()
         key = learn_cache_key(request, response)
         self.assertNotIn(lang, key, "Cache keys shouldn't include the language name when i18n isn't active")