diff --git a/tox.ini b/tox.ini
index 6aeca50..3c9791c 100644
--- a/tox.ini
+++ b/tox.ini
@@ -10,7 +10,9 @@ envlist = py27, py33, py34, py35, py36
 commands =
     py.test {posargs:-v --cov pipdeptree --cov-report xml --cov-report html --cov-report term-missing tests/}
 deps =
+    tox==3.0.0
     graphviz
     pip>=8.0.2
-    pytest
+    pluggy==0.6.0
+    pytest==3.5.0
     pytest-cov