diff --git a/lib/bundler/rubygems_ext.rb b/lib/bundler/rubygems_ext.rb
index 0cd94d60ce..fa61664a90 100644
--- a/lib/bundler/rubygems_ext.rb
+++ b/lib/bundler/rubygems_ext.rb
@@ -1,7 +1,5 @@
 # frozen_string_literal: true
 
-require "pathname"
-
 require "rubygems" unless defined?(Gem)
 
 # We can't let `Gem::Source` be autoloaded in the `Gem::Specification#source`
@@ -47,7 +45,7 @@ module Gem
 
     def full_gem_path
       if source.respond_to?(:root)
-        Pathname.new(loaded_from).dirname.expand_path(source.root).to_s
+        File.expand_path(File.dirname(loaded_from), source.root)
       else
         rg_full_gem_path
       end