diff --git a/Formula/rbenv-default-gems.rb b/Formula/rbenv-default-gems.rb
index 451809feca..3f8d461fbe 100644
--- a/Formula/rbenv-default-gems.rb
+++ b/Formula/rbenv-default-gems.rb
@@ -17,7 +17,7 @@ class RbenvDefaultGems < Formula
 
   def caveats; <<-EOS.undent
     If you are using Homebrew's directories for `rbenv` rather than ~/.rbenv
-    place the `default-gems` file in #{opt_prefix}/.
+    place the `default-gems` file in #{HOMEBREW_PREFIX+'opt/rbenv'}/.
     EOS
   end
 end