diff --git a/Library/Homebrew/requirements/macos_requirement.rb b/Library/Homebrew/requirements/macos_requirement.rb
index a723dda2c6..f8bdcf9150 100644
--- a/Library/Homebrew/requirements/macos_requirement.rb
+++ b/Library/Homebrew/requirements/macos_requirement.rb
@@ -2,6 +2,9 @@
 
 require "requirement"
 
+# A requirement on macOS.
+#
+# @api private
 class MacOSRequirement < Requirement
   fatal true