diff --git a/nixos/modules/services/continuous-integration/buildbot/master.nix b/nixos/modules/services/continuous-integration/buildbot/master.nix
index e1950b91382..d30d94c53cc 100644
--- a/nixos/modules/services/continuous-integration/buildbot/master.nix
+++ b/nixos/modules/services/continuous-integration/buildbot/master.nix
@@ -223,6 +223,7 @@ in {
       };
 
       pythonPackages = mkOption {
+        type = types.listOf types.package;
         default = pythonPackages: with pythonPackages; [ ];
         defaultText = "pythonPackages: with pythonPackages; [ ]";
         description = "Packages to add the to the PYTHONPATH of the buildbot process.";