diff --git a/pkgs/development/ruby-modules/gem-config/default.nix b/pkgs/development/ruby-modules/gem-config/default.nix
index 41fcc336c135..115739bd404d 100644
--- a/pkgs/development/ruby-modules/gem-config/default.nix
+++ b/pkgs/development/ruby-modules/gem-config/default.nix
@@ -524,8 +524,11 @@ in
     '';
   };
 
-   zookeeper = attrs: {
-     buildInputs = stdenv.lib.optionals stdenv.isDarwin [ darwin.cctools ];
-   };
+  zlib = attrs: {
+    buildInputs = [ zlib ];
+  };
 
+  zookeeper = attrs: {
+    buildInputs = stdenv.lib.optionals stdenv.isDarwin [ darwin.cctools ];
+  };
 }