diff --git a/pelican/tests/test_importer.py b/pelican/tests/test_importer.py
index f45f885c..0d9586f0 100644
--- a/pelican/tests/test_importer.py
+++ b/pelican/tests/test_importer.py
@@ -1,12 +1,9 @@
-import datetime
 import locale
 import os
 import re
 from posixpath import join as posix_join
 from unittest.mock import patch
 
-import dateutil.tz
-
 from pelican.settings import DEFAULT_CONFIG
 from pelican.tests.support import (mute, skipIfNoExecutable, temporary_folder,
                                    unittest)
@@ -46,12 +43,9 @@ class TestWithOsDefaults(unittest.TestCase):
     def setUp(self):
         self.old_locale = locale.setlocale(locale.LC_ALL)
         locale.setlocale(locale.LC_ALL, 'C')
-        self.old_timezone = datetime.datetime.now(dateutil.tz.tzlocal()).tzname()
-        os.environ['TZ'] = 'UTC'
 
     def tearDown(self):
         locale.setlocale(locale.LC_ALL, self.old_locale)
-        os.environ['TZ'] = self.old_timezone
 
 
 @skipIfNoExecutable(['pandoc', '--version'])
@@ -502,7 +496,7 @@ class TestTumblrImporter(TestWithOsDefaults):
                 {
                     "type": "photo",
                     "blog_name": "testy",
-                    "date": "2019-11-07 21:26:40 GMT",
+                    "date": "2019-11-07 21:26:40 UTC",
                     "timestamp": 1573162000,
                     "format": "html",
                     "slug": "a-slug",
@@ -528,7 +522,7 @@ class TestTumblrImporter(TestWithOsDefaults):
         self.assertEqual(
             [('Photo',
               '<img alt="" src="https://..fccdc2360ba7182a.jpg" />\n',
-              '2019-11-07-a-slug', '2019-11-07 21:26:40', 'testy', ['photo'],
+              '2019-11-07-a-slug', '2019-11-07 21:26:40+0000', 'testy', ['photo'],
               ['economics'], 'published', 'article', 'html')],
             posts,
             posts)
@@ -544,7 +538,7 @@ class TestTumblrImporter(TestWithOsDefaults):
                     "type": "video",
                     "blog_name": "testy",
                     "slug": "the-slug",
-                    "date": "2017-07-07 20:31:41 GMT",
+                    "date": "2017-07-07 20:31:41 UTC",
                     "timestamp": 1499459501,
                     "state": "published",
                     "format": "html",
@@ -583,7 +577,7 @@ class TestTumblrImporter(TestWithOsDefaults):
               '<iframe>2</iframe>\n'
               '<iframe>3</iframe>\n',
               '2017-07-07-the-slug',
-              '2017-07-07 20:31:41', 'testy', ['video'], [], 'published',
+              '2017-07-07 20:31:41+0000', 'testy', ['video'], [], 'published',
               'article', 'html')],
             posts,
             posts)
@@ -599,7 +593,7 @@ class TestTumblrImporter(TestWithOsDefaults):
                     "type": "video",
                     "blog_name": "testy",
                     "slug": "the-slug",
-                    "date": "2016-08-14 16:37:35 GMT",
+                    "date": "2016-08-14 16:37:35 UTC",
                     "timestamp": 1471192655,
                     "state": "published",
                     "format": "html",
@@ -638,7 +632,7 @@ class TestTumblrImporter(TestWithOsDefaults):
               'v=b">via</a></p>\n<p>Caption</p>'
               '<p>(This video isn\'t available anymore.)</p>\n',
               '2016-08-14-the-slug',
-              '2016-08-14 16:37:35', 'testy', ['video'], ['interviews'],
+              '2016-08-14 16:37:35+0000', 'testy', ['video'], ['interviews'],
               'published', 'article', 'html')],
             posts,
             posts)
diff --git a/pelican/tools/pelican_import.py b/pelican/tools/pelican_import.py
index 16ce6305..44568161 100755
--- a/pelican/tools/pelican_import.py
+++ b/pelican/tools/pelican_import.py
@@ -1,6 +1,7 @@
 #!/usr/bin/env python
 
 import argparse
+import datetime
 import logging
 import os
 import re
@@ -416,10 +417,12 @@ def tumblr2fields(api_key, blogname):
             slug = post.get('slug') or slugify(title, regex_subs=subs)
             tags = post.get('tags')
             timestamp = post.get('timestamp')
-            date = SafeDatetime.fromtimestamp(int(timestamp)).strftime(
-                "%Y-%m-%d %H:%M:%S")
-            slug = SafeDatetime.fromtimestamp(int(timestamp)).strftime(
-                "%Y-%m-%d-") + slug
+            date = SafeDatetime.fromtimestamp(
+                int(timestamp), tz=datetime.timezone.utc
+            ).strftime("%Y-%m-%d %H:%M:%S%z")
+            slug = SafeDatetime.fromtimestamp(
+                int(timestamp), tz=datetime.timezone.utc
+            ).strftime("%Y-%m-%d-") + slug
             format = post.get('format')
             content = post.get('body')
             type = post.get('type')