diff --git a/dev-requirements.txt b/dev-requirements.txt
index 6a51167..772a8bf 100644
--- a/dev-requirements.txt
+++ b/dev-requirements.txt
@@ -1,4 +1,5 @@
 tox==3.9.0
+virtualenv==15.1.0
 wheel==0.34.2
 bump2version==1.0.0
 twine==1.15.0