diff --git a/Library/Homebrew/extend/array.rb b/Library/Homebrew/extend/array.rb
index 7e4b430db9..0163a2bb7f 100644
--- a/Library/Homebrew/extend/array.rb
+++ b/Library/Homebrew/extend/array.rb
@@ -12,6 +12,11 @@ class Array
   #   %w( a b c d e ).third # => "c"
   def third = self[2]
 
+  # Equal to <tt>self[3]</tt>.
+  #
+  #   %w( a b c d e ).fourth # => "d"
+  def fourth = self[3]
+
   # Converts the array to a comma-separated sentence where the last element is
   # joined by the connector word.
   #
diff --git a/Library/Homebrew/extend/array.rbi b/Library/Homebrew/extend/array.rbi
index 5255357ead..0c1bb89dd7 100644
--- a/Library/Homebrew/extend/array.rbi
+++ b/Library/Homebrew/extend/array.rbi
@@ -6,4 +6,7 @@ class Array
 
   sig { returns(T.nilable(Elem)) }
   def third; end
+
+  sig { returns(T.nilable(Elem)) }
+  def fourth; end
 end