diff --git a/Library/Homebrew/utils.rb b/Library/Homebrew/utils.rb
index 68557474de..7a7673d017 100644
--- a/Library/Homebrew/utils.rb
+++ b/Library/Homebrew/utils.rb
@@ -377,7 +377,8 @@ ensure
 end
 
 def capture_stderr
-  old, $stderr = $stderr, StringIO.new
+  old = $stderr
+  $stderr = StringIO.new
   yield
   $stderr.string
 ensure