diff --git a/newsfragments/3623.minor b/newsfragments/3623.minor
new file mode 100644
index 000000000..8b1378917
--- /dev/null
+++ b/newsfragments/3623.minor
@@ -0,0 +1 @@
+
diff --git a/tox.ini b/tox.ini
index b4c895035..77f5faede 100644
--- a/tox.ini
+++ b/tox.ini
@@ -124,6 +124,10 @@ deps =
     mypy
     git+https://github.com/Shoobx/mypy-zope
     git+https://github.com/warner/foolscap
+    # Twisted 21.2.0 introduces some type hints which we are not yet
+    # compatible with.
+    # https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3622
+    twisted<21.2.0
 commands = mypy src