diff --git a/pkgs/development/interpreters/ruby/default.nix b/pkgs/development/interpreters/ruby/default.nix
index f3d4ae4bb00..60076455dae 100644
--- a/pkgs/development/interpreters/ruby/default.nix
+++ b/pkgs/development/interpreters/ruby/default.nix
@@ -83,7 +83,7 @@ let
 
         enableParallelBuilding = true;
 
-        hardeningDisable = lib.optional isRuby20 [ "format" ];
+        hardeningDisable = lib.optional isRuby20 "format";
 
         patches =
           (import ./patchsets.nix {