diff --git a/doc/lispref/modes.texi b/doc/lispref/modes.texi
index 421ec136c7c..c5c6c10a6fa 100644
--- a/doc/lispref/modes.texi
+++ b/doc/lispref/modes.texi
@@ -1861,7 +1861,17 @@ marking the @code{define-minor-mode} form as autoloaded.
 @item :init-value @var{init-value}
 This is the value to which the @var{mode} variable is initialized.
 Except in unusual circumstances (see below), this value must be
-@code{nil}.
+@code{nil}.  If the mode is global (see below), and the initial value is
+@code{t}, i.e., the mode is turned on by default, you should consider
+forcing Emacs to run the mode function at startup, like this:
+
+@lisp
+ :initialize #'custom-initialize-delay
+@end lisp
+
+@noindent
+otherwise, the minor mode might not appear in the @file{*Help*} buffer
+generated by @kbd{C-h m} (@pxref{Mode Help}).
 
 @item :lighter @var{lighter}
 The string @var{lighter} says what to display in the mode line