diff --git a/array.rb b/array.rb
index a43a3b27b1..05ce60773e 100644
--- a/array.rb
+++ b/array.rb
@@ -49,6 +49,8 @@ class Array
   # But +self+ may contain duplicates:
   #    a = [1, 1, 1, 2, 2, 3]
   #    a.sample(a.size * 2) # => [1, 1, 3, 2, 1, 2]
+  # The argument +n+ must be a non-negative numeric value.
+  # The order of the result array is unrelated to the order of +self+.
   # Returns a new empty \Array if +self+ is empty.
   #
   # The optional +random+ argument will be used as the random number generator: