diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index 6605ff0a70..98e8ba719b 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -52,9 +52,9 @@ class Formula
   attr_reader :head
 
   # The currently active {SoftwareSpec}.
-  # Defaults to stable unless `--devel` or `--HEAD` is passed.
-  # @private
+  # @see #determine_active_spec
   attr_reader :active_spec
+  protected :active_spec
 
   # The {PkgVersion} for this formula with version and {#revision} information.
   attr_reader :pkg_version