diff --git a/pkgs/development/python-modules/validators/default.nix b/pkgs/development/python-modules/validators/default.nix
index 29ec9cd73d73..f83fe801a2a2 100644
--- a/pkgs/development/python-modules/validators/default.nix
+++ b/pkgs/development/python-modules/validators/default.nix
@@ -3,6 +3,7 @@
 , fetchPypi
 , isPy27
 , decorator
+, six
 , pytestCheckHook
 }:
 
@@ -18,6 +19,7 @@ buildPythonPackage rec {
 
   propagatedBuildInputs = [
     decorator
+    six
   ];
 
   checkInputs = [