diff --git a/tests/constraints.txt b/tests/constraints.txt
new file mode 100644
index 000000000..3bc30de15
--- /dev/null
+++ b/tests/constraints.txt
@@ -0,0 +1 @@
+Twisted!=18.4.0
diff --git a/tox.ini b/tox.ini
index 60ff8c15e..c2fa9af28 100644
--- a/tox.ini
+++ b/tox.ini
@@ -8,6 +8,7 @@ envlist = py27
 
 [testenv]
 deps =
+    -ctests/constraints.txt
     -rrequirements.txt
     # Extras
     botocore