diff --git a/activesupport/lib/active_support/testing/performance.rb b/activesupport/lib/active_support/testing/performance.rb
index 7da2f6791a1327faea75ec20748178b511b13e29..b8e4f46d70a2b3d74f9096caf4f57d94ebe2c679 100644
--- a/activesupport/lib/active_support/testing/performance.rb
+++ b/activesupport/lib/active_support/testing/performance.rb
@@ -116,7 +116,7 @@ def environment
             rails = Rails::VERSION::STRING
             if File.directory?('vendor/rails/.git')
               Dir.chdir('vendor/rails') do
-                rails += "#{$1}.#{$2}" if `git branch -v` =~ /^\* (\S+)\s+(\S+)/
+                rails += ".#{$1}.#{$2}" if `git branch -v` =~ /^\* (\S+)\s+(\S+)/
               end
             end