diff --git a/tox.ini b/tox.ini
index c6dd3f477ee..b9c3b6c33da 100644
--- a/tox.ini
+++ b/tox.ini
@@ -146,7 +146,8 @@ deps =
     github3.py
     pre-commit>=2.9.3
     wheel
-    towncrier
+    # Pinned because of twisted/towncrier#346
+    towncrier ==18.6.0
 commands = python scripts/release.py {posargs}
 
 [testenv:prepare-release-pr]