diff --git a/pkgs/wrap-retroarch.nix b/pkgs/wrap-retroarch.nix
index 1abf718..296f46b 100644
--- a/pkgs/wrap-retroarch.nix
+++ b/pkgs/wrap-retroarch.nix
@@ -12,7 +12,7 @@ let
   settings' = { libretro_directory = coresPath; } // settings;
   settingsPath = runCommand "declarative-retroarch.cfg"
     {
-      value = lib.concatStringsSep "\n" (lib.mapAttrsToList (n: v: "${n} = \"${v}\"") settings);
+      value = lib.concatStringsSep "\n" (lib.mapAttrsToList (n: v: "${n} = \"${v}\"") settings');
       passAsFile = [ "value" ];
     }
     ''
@@ -20,8 +20,8 @@ let
     '';
   coresPath = let
     path = assert
-      lib.assertMsg (builtins.length (map (c: c.libretroCore) cores) == 1)
-      "Libretro cores are not under the same paths"; 
+      lib.assertMsg (builtins.length (lib.unique (map (c: c.libretroCore) cores)) == 1)
+      "Libretro cores are not under the same paths: ${builtins.toString (lib.unique (builtins.map (c: c.libretroCore) cores))}";
     (builtins.head cores).libretroCore;
   in
     symlinkJoin {
@@ -43,7 +43,6 @@ symlinkJoin {
   };
 
   postBuild = ''
-    # wrap binary to load cores from the proper location(s)
     wrapProgram $out/bin/retroarch ${wrapperArgs}
   '';