Gemfile in vagrant-skytap-0.3.5 vs Gemfile in vagrant-skytap-0.3.6

@@ -1,22 +1,27 @@
 source "https://rubygems.org"
 
 gemspec
 
+VAGRANT_GEM_TAG = ENV['VAGRANT_GEM_TAG'] || 'v1.7.4'
+# vagrant-spec made a change in 1d09951e which created a dependency conflict
+# in our test environment. For now, default to the preceding revision.
+VAGRANT_SPEC_GEM_REF = ENV['VAGRANT_SPEC_REF'] || '5006bc73'
+
 group :development do
   # We depend on Vagrant for development, but we don't add it as a
   # gem dependency because we expect to be installed within the
   # Vagrant environment itself using `vagrant plugin`.
   if File.exist?(File.expand_path("../../vagrant", __FILE__))
     gem 'vagrant', path: "../vagrant"
   else
-    gem "vagrant", :git => "git://github.com/mitchellh/vagrant.git", :tag => 'v1.7.2'
+    gem "vagrant", :git => "git://github.com/mitchellh/vagrant.git", tag: VAGRANT_GEM_TAG
   end
 
   if File.exist?(File.expand_path("../../vagrant-spec", __FILE__))
     gem 'vagrant-spec', path: "../vagrant-spec"
   else
-    gem 'vagrant-spec', git: "https://github.com/mitchellh/vagrant-spec.git"
+    gem 'vagrant-spec', git: "https://github.com/mitchellh/vagrant-spec.git", ref: VAGRANT_SPEC_GEM_REF
   end
 
   gem "rspec-expectations", "~> 2.14.0"
 end