diff --git a/src/process.c b/src/process.c
index 5144c5d6c92..cab8a1d5cf2 100644
--- a/src/process.c
+++ b/src/process.c
@@ -6795,10 +6795,13 @@ emacs_get_tty_pgrp (struct Lisp_Process *p)
 
 DEFUN ("process-running-child-p", Fprocess_running_child_p,
        Sprocess_running_child_p, 0, 1, 0,
-       doc: /* Return non-nil if PROCESS has given the terminal to a
-child.  If the operating system does not make it possible to find out,
-return t.  If we can find out, return the numeric ID of the foreground
-process group.  */)
+       doc: /* Return non-nil if PROCESS has given control of its terminal to a child.
+If the operating system does not make it possible to find out, return t.
+If it's possible to find out, return the numeric ID of the foreground
+process group if PROCESS did give control of its terminal to a
+child process, and return nil if it didn't.
+
+PROCESS must be a real subprocess, not a connection.  */)
   (Lisp_Object process)
 {
   /* Initialize in case ioctl doesn't exist or gives an error,