diff --git a/ChangeLog b/ChangeLog
index e6842f10c6..a761046917 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Feb 20 07:51:19 2013  Eric Hodel  <drbrain@segment7.net>
+
+	* lib/rubygems/installer.rb:  Use gsub instead of gsub! to avoid
+	  altering @bin_dir.  Fixes tests on windows.  [ruby-trunk - Bug #7885]
+
 Tue Feb 19 20:50:00 2013  Kenta MURATA  <mrkn@mrkn.jp>
 
 	* ext/bigdecimal/bigdecimal.gemspec: bump to 1.2.0.
diff --git a/lib/rubygems/installer.rb b/lib/rubygems/installer.rb
index a9ab4c7a5b..0865a6dd3d 100644
--- a/lib/rubygems/installer.rb
+++ b/lib/rubygems/installer.rb
@@ -561,7 +561,9 @@ class Gem::Installer
   # DOC: Missing docs or :nodoc:.
   def check_that_user_bin_dir_is_in_path
     user_bin_dir = @bin_dir || Gem.bindir(gem_home)
-    user_bin_dir.gsub!(File::SEPARATOR, File::ALT_SEPARATOR) if File::ALT_SEPARATOR
+    user_bin_dir = user_bin_dir.gsub(File::SEPARATOR, File::ALT_SEPARATOR) if
+      File::ALT_SEPARATOR
+
     path = ENV['PATH']
     if Gem.win_platform? then
       path = path.downcase