1 files changed, 1 insertions, 0 deletions
diff --git a/lib/set.rb b/lib/set.rb
index 586a5d9f4d..0ad47c842f 100644
--- a/lib/set.rb
+++ b/lib/set.rb
@@ -519,6 +519,7 @@ end
 
 module Enumerable
   # Makes a set from the enumerable object with given arguments.
+  # Needs to +require "set"+ to use this method.
   def to_set(klass = Set, *args, &block)
     klass.new(self, *args, &block)
   end