diff --git a/nix/modules/unit/lisp/fpkg.el b/nix/modules/unit/lisp/fpkg.el
index a3ef3bf..0415151 100644
--- a/nix/modules/unit/lisp/fpkg.el
+++ b/nix/modules/unit/lisp/fpkg.el
@@ -98,7 +98,12 @@ same NAME is set to t."
 
 
 (defmacro try! (pkg &rest details)
-  "Try the PKG with the given DETAILS in the running session."
+  "Try the PKG with the given DETAILS in the running session.
+
+It will install the package using Nix and make it available to the current
+running session.  For a persistant installation use `use!'."
+  (declare (indent defun))
+
   (let ((flake-dir (format "%s/share/fg42" (fg42-path)))
         (cwd (getenv "PWD")))
     (cd flake-dir)
@@ -107,7 +112,7 @@ same NAME is set to t."
            (out (car (string-split output "\n" t))))
       (add-emacs-vars out)
       (cd cwd)
-      out)))
+      `(use-package ,pkg ,@details))))
 
 
 (provide 'fpkg)