diff --git a/src/base.janet b/src/base.janet
index c0fee40..95203dd 100644
--- a/src/base.janet
+++ b/src/base.janet
@@ -130,8 +130,12 @@
   (string/join (map (fn [x] (-> x first show-patt)) clauses) "\n"))
 
 (defn doc [fnn]
-  (def {:name name :doc doc} fnn)
-  (string/join [name (pretty-patterns fnn) doc] "\n"))
+  (when (not= :fn (ludus/type fnn)) (break "No documentation available."))
+  (def {:name name :doc docstring} fnn)
+  (string/join [name 
+                (pretty-patterns fnn) 
+                (if docstring docstring "No docstring available.")] 
+    "\n"))
 
 (defn- conj!-set [sett value]
   (set (sett value) true)