diff --git a/Library/Homebrew/extend/pathname.rb b/Library/Homebrew/extend/pathname.rb
index 33db3eed66..59061af88e 100644
--- a/Library/Homebrew/extend/pathname.rb
+++ b/Library/Homebrew/extend/pathname.rb
@@ -298,7 +298,7 @@ class Pathname
 
   def / that
     self + that.to_s
-  end
+  end unless method_defined?(:/)
 
   def ensure_writable
     saved_perms = nil