1 files changed, 2 insertions, 0 deletions

diff --git a/src/doc.c b/src/doc.c
index d27fa3f792d..3832eb3708d 100644
--- a/src/doc.c
+++ b/src/doc.c
@@ -347,6 +347,8 @@ string is passed through `substitute-command-keys'.  */)
     {
       if (XSUBR (fun)->doc == 0)
         return Qnil;
+      /* FIXME: This is not portable, as it assumes that string
+         pointers have the top bit clear.  */
       else if ((EMACS_INT) XSUBR (fun)->doc >= 0)
         doc = build_string (XSUBR (fun)->doc);
       else