diff --git a/Library/Homebrew/cask/lib/hbc/download_strategy.rb b/Library/Homebrew/cask/lib/hbc/download_strategy.rb
index 245ad4adeb..c6f4b78543 100644
--- a/Library/Homebrew/cask/lib/hbc/download_strategy.rb
+++ b/Library/Homebrew/cask/lib/hbc/download_strategy.rb
@@ -154,7 +154,7 @@ module Hbc
     end
 
     def ext
-      Pathname.new(@url).extname[/[^?]+/]
+      Pathname.new(@url).extname[/[^?&]+/]
     end
   end