diff --git a/pkgs/lib/types.nix b/pkgs/lib/types.nix
index b62c08f3af5..f9a195a80ba 100644
--- a/pkgs/lib/types.nix
+++ b/pkgs/lib/types.nix
@@ -166,7 +166,7 @@ rec {
         if length list == 1 then
           head list
         else
-          throw "Multiple definitions. Only one is allowed for this option.";
+          throw "Multiple definitions of ${elemType.name}. Only one is allowed for this option.";
     };
 
     none = elemType: mkOptionType {