diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -56,7 +56,7 @@ requirements = [
     "Whoosh >= 2.5.0, < 2.8",
     "celery >= 3.1, < 4.0", # TODO: celery 4 doesn't work
     "Babel >= 1.3, < 2.8",
-    "python-dateutil >= 1.5.0, < 2.9",
+    "python-dateutil >= 2.1.0, < 2.9",
     "Markdown >= 2.2.1, < 3.2",
     "docutils >= 0.11, < 0.15",
     "URLObject >= 2.3.4, < 2.5",