diff --git a/pkgs/development/interpreters/ruby/build-ruby-gem/default.nix b/pkgs/development/interpreters/ruby/build-ruby-gem/default.nix
index c5b9fba37aa0..effd343ecfd9 100644
--- a/pkgs/development/interpreters/ruby/build-ruby-gem/default.nix
+++ b/pkgs/development/interpreters/ruby/build-ruby-gem/default.nix
@@ -50,24 +50,24 @@ lib.makeOverridable (
 , passthru ? {}
 , ...} @ attrs:
 
-if ! builtins.elem type [ "git" "gem" ]
-then throw "buildRubyGem: don't know how to build a gem of type \"${type}\""
-else
-
 let
   shellEscape = x: "'${lib.replaceChars ["'"] [("'\\'" + "'")] x}'";
   rubygems = (attrs.rubygems or defs.rubygems).override {
     inherit ruby;
   };
   src = attrs.src or (
-    if type == "gem"
-    then fetchurl {
-      urls = map (remote: "${remote}/gems/${gemName}-${version}.gem") remotes;
-      inherit (attrs) sha256;
-    } else fetchgit {
-      inherit (attrs) url rev sha256 fetchSubmodules;
-      leaveDotGit = true;
-    }
+    if type == "gem" then
+      fetchurl {
+        urls = map (remote: "${remote}/gems/${gemName}-${version}.gem") remotes;
+        inherit (attrs) sha256;
+      }
+    else if type == "git" then
+      fetchgit {
+        inherit (attrs) url rev sha256 fetchSubmodules;
+        leaveDotGit = true;
+      }
+    else
+      throw "buildRubyGem: don't know how to build a gem of type \"${type}\""
   );
   documentFlag =
     if document == []
diff --git a/pkgs/development/interpreters/ruby/gemconfig/default.nix b/pkgs/development/interpreters/ruby/gemconfig/default.nix
index 787c3be54e35..dd4ae725095d 100644
--- a/pkgs/development/interpreters/ruby/gemconfig/default.nix
+++ b/pkgs/development/interpreters/ruby/gemconfig/default.nix
@@ -21,6 +21,7 @@
 , libiconv, postgresql, v8_3_16_14, clang, sqlite, zlib, imagemagick
 , pkgconfig , ncurses, xapian, gpgme, utillinux, fetchpatch, tzdata, icu, libffi
 , cmake, libssh2, openssl, mysql, darwin, git, perl, gecode_3, curl
+, libmsgpack
 }:
 
 let
@@ -40,6 +41,10 @@ in
     '';
   };
 
+  eventmachine = attrs: {
+    buildInputs = [ openssl ];
+  };
+
   ffi = attrs: {
     buildInputs = [ libffi pkgconfig ];
   };
@@ -56,6 +61,10 @@ in
     buildFlags = [ "--with-system-v8=true" ];
   };
 
+  msgpack = attrs: {
+    buildInputs = [ libmsgpack ];
+  };
+
   mysql2 = attrs: {
     buildInputs = [ mysql.lib zlib openssl ];
   };