diff --git a/tox.ini b/tox.ini
index f75ec08a1..8fa10e806 100644
--- a/tox.ini
+++ b/tox.ini
@@ -21,7 +21,7 @@ passenv = DISPLAY
 setenv = PYTHONPATH = {env:PWD}:
 sitepackages = True
 deps =
-    twisted
+    twisted==16.6
     service_identity
     mako
     chardet