diff --git a/lib/rubygems/test_case.rb b/lib/rubygems/test_case.rb
index e2a880ef2b..cd74ec614c 100644
--- a/lib/rubygems/test_case.rb
+++ b/lib/rubygems/test_case.rb
@@ -302,7 +302,6 @@ class Gem::TestCase < Minitest::Test
     ENV['GEM_VENDOR'] = nil
     ENV['GEMRC'] = nil
     ENV['SOURCE_DATE_EPOCH'] = nil
-    ENV["TMPDIR"] = File.expand_path("tmp")
 
     @current_dir = Dir.pwd
     @fetcher     = nil