diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -54,7 +54,7 @@ requirements = [
     "Mako >= 0.9.1, < 1.2",
     "Pygments >= 2.2.0, < 2.6",
     "Whoosh >= 2.7.1, < 2.8",
-    "celery >= 3.1, < 4.0", # TODO: celery 4 doesn't work
+    "celery >= 4.3, < 4.5",
     "Babel >= 1.3, < 2.9",
     "python-dateutil >= 2.1.0, < 2.9",
     "Markdown >= 2.2.1, < 3.2",