diff --git a/lib/uri/common.rb b/lib/uri/common.rb
index b1a47cf..411a7e3 100644
--- a/lib/uri/common.rb
+++ b/lib/uri/common.rb
@@ -889,6 +889,7 @@ module Kernel
   # Returns a \URI object derived from the given +uri+,
   # which may be a \URI string or an existing \URI object:
   #
+  #   require 'uri'
   #   # Returns a new URI.
   #   uri = URI('http://github.com/ruby/ruby')
   #   # => #<URI::HTTP http://github.com/ruby/ruby>
@@ -896,6 +897,8 @@ module Kernel
   #   URI(uri)
   #   # => #<URI::HTTP http://github.com/ruby/ruby>
   #
+  # You must require 'uri' to use this method.
+  #
   def URI(uri)
     if uri.is_a?(URI::Generic)
       uri