diff --git a/requirements.txt b/requirements.txt
index 62a20196..71814bd8 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,6 +1,7 @@
 PyYAML==3.12
 
 # Testing
+tox==2.3.1
 pytest==3.0.3
 pytest-cov==2.3.1
 coverage==4.2