diff --git a/Library/Homebrew/download_strategy.rb b/Library/Homebrew/download_strategy.rb
index 17931f21df..d1564f9778 100644
--- a/Library/Homebrew/download_strategy.rb
+++ b/Library/Homebrew/download_strategy.rb
@@ -217,7 +217,7 @@ class SubversionDownloadStrategy < AbstractDownloadStrategy
       @co = Pathname.new("#{HOMEBREW_CACHE}/#{name}--svn")
     end
 
-    @co += "-HEAD" if ARGV.build_head?
+    @co = Pathname.new(@co.to_s + '-HEAD') if ARGV.build_head?
   end
 
   def cached_location