diff --git a/lib/bundled_gems.rb b/lib/bundled_gems.rb
index 6a20f51958..4427eeb873 100644
--- a/lib/bundled_gems.rb
+++ b/lib/bundled_gems.rb
@@ -52,7 +52,7 @@ module Gem::BUNDLED_GEMS
   WARNED = {}                   # unfrozen
 
   conf = ::RbConfig::CONFIG
-  if !File.exist?(conf["rubylibdir"])
+  if ENV["TEST_BUNDLED_GEMS"]
     LIBDIR = (File.expand_path(File.join(__dir__, "..", "lib")) + "/").freeze
   else
     LIBDIR = (conf["rubylibdir"] + "/").freeze
diff --git a/spec/bundler/bundled_gems_spec.rb b/spec/bundler/bundled_gems_spec.rb
index 746a7c695b..f2f908b341 100644
--- a/spec/bundler/bundled_gems_spec.rb
+++ b/spec/bundler/bundled_gems_spec.rb
@@ -1,6 +1,8 @@
 require "bundled_gems"
 
 RSpec.describe "bundled_gems.rb" do
+  ENV["TEST_BUNDLED_GEMS"] = "true"
+
   def script(code, options = {})
     options[:artifice] ||= "compact_index"
     ruby("require 'bundler/inline'\n\n" + code, options)