diff --git a/pkgs/development/interpreters/ruby/gem.nix b/pkgs/development/interpreters/ruby/gem.nix
index 124c7cd747f..b4ddd26bb46 100644
--- a/pkgs/development/interpreters/ruby/gem.nix
+++ b/pkgs/development/interpreters/ruby/gem.nix
@@ -44,6 +44,8 @@ let
 
     propagatedUserEnvPkgs = requiredGems;
 
+    passthru.isRubyGem = true;
+
   };
   mb = stdenv.lib.maybeAttr;
   patchedGem = a: stdenv.mkDerivation (removeAttrs (stdenv.lib.mergeAttrsByFuncDefaults