diff --git a/Library/Homebrew/compat/extend/string.rb b/Library/Homebrew/compat/extend/string.rb
index 0795ab376a..b704cd2b5f 100644
--- a/Library/Homebrew/compat/extend/string.rb
+++ b/Library/Homebrew/compat/extend/string.rb
@@ -1,6 +1,7 @@
 class String
   def undent
     odisabled "<<-EOS.undent", "<<~EOS"
+    self
   end
   alias unindent undent