diff --git a/Gemfile b/Gemfile
index 3096ef61..317ae33f 100644
--- a/Gemfile
+++ b/Gemfile
@@ -2,8 +2,8 @@ source 'https://rubygems.org'
 
 gemspec
 
-gem 'immutable', :git => 'https://github.com/dkubb/immutable'
-gem 'abstract',  :git => 'https://github.com/mbj/abstract'
+gem 'immutable', :git => 'https://github.com/dkubb/immutable.git', :ref => '4a4b7ddd138a32944fa0ddaff8412490cf9dd875'
+gem 'abstract',  :git => 'https://github.com/mbj/abstract.git'
 
 # Until there is a release with explicit sends to self fix
 gem 'to_source', :git => 'https://github.com/mbj/to_source'