diff --git a/lisp/help-fns.el b/lisp/help-fns.el
index 5cc8df6497f..98231614d71 100644
--- a/lisp/help-fns.el
+++ b/lisp/help-fns.el
@@ -112,6 +112,7 @@ current help buffer.")
   (pcase-dolist (`(,prefix . ,files) prefixes)
     (setq help-definition-prefixes
           (radix-tree-insert help-definition-prefixes prefix nil))
+    (remhash prefix definition-prefixes)
     (dolist (file files)
       ;; FIXME: Should we scan help-definition-prefixes to remove
       ;; other prefixes of the same file?