diff --git a/Library/Homebrew/dev-cmd/bump-cask-pr.rb b/Library/Homebrew/dev-cmd/bump-cask-pr.rb
index c3a0cf1e63..64c6773558 100644
--- a/Library/Homebrew/dev-cmd/bump-cask-pr.rb
+++ b/Library/Homebrew/dev-cmd/bump-cask-pr.rb
@@ -190,7 +190,7 @@ module Homebrew
 
       replacement_pairs << [
         /#{Regexp.escape(old_base_url)}/,
-        new_base_url,
+        new_base_url.to_s,
       ]
     end