diff --git a/nixos/modules/services/development/hoogle.nix b/nixos/modules/services/development/hoogle.nix
index 7c635f7a5b8d..7c2a1c8e1624 100644
--- a/nixos/modules/services/development/hoogle.nix
+++ b/nixos/modules/services/development/hoogle.nix
@@ -40,6 +40,7 @@ in {
 
     haskellPackages = mkOption {
       description = "Which haskell package set to use.";
+      type = types.attrs;
       default = pkgs.haskellPackages;
       defaultText = literalExpression "pkgs.haskellPackages";
     };