diff --git a/tox.ini b/tox.ini
index 5d9964ba..15e72a0d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -5,8 +5,9 @@ envlist = py{27,34,35,36}
 pep8ignore = test_* E402
 
 [testenv]
+# see https://github.com/pytest-dev/pytest/issues/2957 for the pytest pinning reason
 deps=
-  pytest
+  pytest<3.3.0
   pytest-pep8
   pytest-cov
   mock