diff --git a/tox.ini b/tox.ini
index 60b19f15..dbfc0744 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,6 +1,6 @@
 [tox]
 envlist = py35,py36,py37
-skip_missing_interpreters=true
+skip_missing_interpreters = True
 skipsdist = True
 minversion = 3.10.0