patch by MSP-Greg
diff --git a/lib/rubygems/bundler_version_finder.rb b/lib/rubygems/bundler_version_finder.rb
index baca170840..77664113bf 100644
--- a/lib/rubygems/bundler_version_finder.rb
+++ b/lib/rubygems/bundler_version_finder.rb
@@ -102,7 +102,7 @@ def self.lockfile_contents
     lockfile = case gemfile
     when "gems.rb" then "gems.locked"
     else "#{gemfile}.lock"
-    end.untaint
+    end.dup.untaint
 
     return unless File.file?(lockfile)