diff --git a/Library/Homebrew/cask/lib/hbc/download_strategy.rb b/Library/Homebrew/cask/lib/hbc/download_strategy.rb
index 28ae704ee0..016bb66e6e 100644
--- a/Library/Homebrew/cask/lib/hbc/download_strategy.rb
+++ b/Library/Homebrew/cask/lib/hbc/download_strategy.rb
@@ -185,7 +185,7 @@ module Hbc
     end
 
     def ext
-      Pathname.new(@url).extname
+      Pathname.new(@url).extname[/[^?]+/]
     end
   end