diff --git a/tools/gendoc.janet b/tools/gendoc.janet
index 360082aa..47fbe9df 100644
--- a/tools/gendoc.janet
+++ b/tools/gendoc.janet
@@ -104,6 +104,7 @@
 # Generate parts and print them to stdout
 (def parts (seq [[k entry]
                  :in (sort (pairs (table/getproto (fiber/getenv (fiber/current)))))
+                 :when (symbol? k)
                  :when (and (get entry :doc) (not (get entry :private)))]
                 (emit-item k entry)))
 (print