diff --git a/spec/mspec/tool/sync/sync-rubyspec.rb b/spec/mspec/tool/sync/sync-rubyspec.rb
index 48047e013f..74881c1a77 100644
--- a/spec/mspec/tool/sync/sync-rubyspec.rb
+++ b/spec/mspec/tool/sync/sync-rubyspec.rb
@@ -12,7 +12,6 @@ IMPLS = {
   },
   mri: {
     git: "https://github.com/ruby/ruby.git",
-    master: "trunk",
   },
 }
 
@@ -48,10 +47,6 @@ class RubyImplementation
     @data[:git]
   end
 
-  def default_branch
-    @data[:master] || "master"
-  end
-
   def repo_name
     File.basename(git_url, ".git")
   end
@@ -99,7 +94,7 @@ def update_repo(impl)
   Dir.chdir(impl.repo_name) do
     puts Dir.pwd
 
-    sh "git", "checkout", impl.default_branch
+    sh "git", "checkout", "master"
     sh "git", "pull"
   end
 end