diff --git a/pkgs/development/python-modules/marionette-harness/mozfile.nix b/pkgs/development/python-modules/marionette-harness/mozfile.nix
index 773b0bb8c1e5..9ca8ea0b7891 100644
--- a/pkgs/development/python-modules/marionette-harness/mozfile.nix
+++ b/pkgs/development/python-modules/marionette-harness/mozfile.nix
@@ -1,6 +1,8 @@
 { lib
 , buildPythonPackage
 , fetchPypi
+, isPy27
+, six
 }:
 
 buildPythonPackage rec {
@@ -12,7 +14,7 @@ buildPythonPackage rec {
     sha256 = "e5dc835582ea150e35ecd57e9d86cb707d3aa3b2505679db7332326dd49fd6b8";
   };
 
-  propagatedBuildInputs = [ ];
+  propagatedBuildInputs = lib.optional isPy27 six;
 
   # mozhttpd -> moznetwork -> mozinfo -> mozfile
   doCheck = false;