diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index 0d000496b9..f0b6f70bf3 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -1008,7 +1008,7 @@ class Formula
   # rarely, you don't want your library symlinked into the main prefix
   # see gettext.rb for an example
   def keg_only?
-    keg_only_reason && keg_only_reason.valid?
+    !!keg_only_reason && keg_only_reason.valid?
   end
 
   # @private