diff --git a/doc/lispref/os.texi b/doc/lispref/os.texi
index ccc0f69a12d..bb768fe2da8 100644
--- a/doc/lispref/os.texi
+++ b/doc/lispref/os.texi
@@ -713,7 +713,10 @@ the Emacs process.  (This is useful primarily in batch operation; see
 
 If @var{exit-data} is a string, its contents are stuffed into the
 terminal input buffer so that the shell (or whatever program next reads
-input) can read them.
+input) can read them.  This is only possible on some systems.  Note that
+recent versions of GNU/Linux disable the system API required for
+stuffing the string into the terminal input, so this might not work on
+your system without special privileges.
 
 If @var{exit-data} is neither an integer nor a string, or is omitted,
 that means to use the (system-specific) exit status which indicates
diff --git a/src/emacs.c b/src/emacs.c
index 17c56986083..777ade9d825 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -2947,7 +2947,9 @@ sort_args (int argc, char **argv)
 DEFUN ("kill-emacs", Fkill_emacs, Skill_emacs, 0, 2, "P",
        doc: /* Exit the Emacs job and kill it.
 If ARG is an integer, return ARG as the exit program code.
-If ARG is a string, stuff it as keyboard input.
+If ARG is a string, stuff it as keyboard input.  (This might
+not work on modern systems due to security considerations, or
+not at all.)
 Any other value of ARG, or ARG omitted, means return an
 exit code that indicates successful program termination.