diff --git a/Library/Homebrew/download_strategy.rb b/Library/Homebrew/download_strategy.rb
index 0b7ac2addf..699228d9f0 100644
--- a/Library/Homebrew/download_strategy.rb
+++ b/Library/Homebrew/download_strategy.rb
@@ -1277,7 +1277,7 @@ end
 class BazaarDownloadStrategy < VCSDownloadStrategy
   def initialize(url, name, version, **meta)
     super
-    @url.sub!(%r{^bzr://}, "")
+    @url = @url.sub(%r{^bzr://}, "")
   end
 
   # @see AbstractDownloadStrategy#source_modified_time