diff --git a/Library/Homebrew/formula_versions.rb b/Library/Homebrew/formula_versions.rb
index 2fb219d85d..ecd67d5270 100644
--- a/Library/Homebrew/formula_versions.rb
+++ b/Library/Homebrew/formula_versions.rb
@@ -2,6 +2,9 @@
 
 require "formula"
 
+# Helper class for traversing a formula's previous versions.
+#
+# @api private
 class FormulaVersions
   include Context