diff --git a/test/rubygems/test_gem_installer.rb b/test/rubygems/test_gem_installer.rb
index 9783dbff3eb3..78c69bf7339e 100644
--- a/test/rubygems/test_gem_installer.rb
+++ b/test/rubygems/test_gem_installer.rb
@@ -277,7 +277,8 @@ def test_generate_bin_bindir
   end
 
   def test_generate_bin_bindir_with_user_install_warning
-    bin_dir = Gem.win_platform? ? File.expand_path(ENV["WINDIR"]) : "/usr/bin"
+    bin_dir = Gem.win_platform? ? File.expand_path(ENV["WINDIR"]).upcase :
+                                  "/usr/bin"
 
     options = {
       :bin_dir => bin_dir,