diff --git a/pkgs/development/python-modules/plone-testing/default.nix b/pkgs/development/python-modules/plone-testing/default.nix
index 81482414d57f..636028c957a9 100644
--- a/pkgs/development/python-modules/plone-testing/default.nix
+++ b/pkgs/development/python-modules/plone-testing/default.nix
@@ -1,6 +1,7 @@
 { lib
 , buildPythonPackage
 , fetchPypi
+, six
 , zope_testing
 , setuptools
 }:
@@ -14,7 +15,7 @@ buildPythonPackage rec {
     sha256 = "db71bde0d4d3c273dbba8c7a2ab259a42f038eca74184da36c5aab61e90e8dd7";
   };
 
-  propagatedBuildInputs = [ setuptools zope_testing ];
+  propagatedBuildInputs = [ six setuptools zope_testing ];
 
   # Huge amount of testing dependencies (including Zope2)
   doCheck = false;
@@ -24,4 +25,4 @@ buildPythonPackage rec {
     homepage = https://github.com/plone/plone.testing;
     license = lib.licenses.bsd3;
   };
-}
\ No newline at end of file
+}