diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index 2ef9d62987..14ab534ae1 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -725,6 +725,7 @@ class Formula
 
     # The reason for why this software is not linked (by default) to
     # {::HOMEBREW_PREFIX}.
+    # @api private
     attr_reader :keg_only_reason
 
     # @!attribute [rw]