diff --git a/setup.cfg b/setup.cfg
index a5234d1b..c111fdf6 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -45,6 +45,7 @@ install_requires =
     Babel>=1.3
     celery>=3.0,<4.3.0  # Removed the "sqlite" transport alias in 4.3.0
                         # making tests fail.
+    billiard<3.6.0,>=3.5.0.2  # required by celery
     certifi>=2017.4.17  # Required by requests on Fedora 33 (bin/gmg fails)
     ConfigObj
     email-validator