diff --git a/src/buffer.c b/src/buffer.c
index b72695d82bc..031f5da8e6e 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -5847,7 +5847,11 @@ If the buffer has never been shown in a window, the value is nil.  */);
 	       doc: /* *Non-nil means deactivate the mark when the buffer contents change.
 Non-nil also enables highlighting of the region whenever the mark is active.
 The variable `highlight-nonselected-windows' controls whether to highlight
-all windows or just the selected window.  */);
+all windows or just the selected window.
+
+If the value is `lambda', that enables Transient Mark mode temporarily
+until the next buffer modification.  If a command sets the value to `only',
+that enables Transient Mark mode for the following command only.  */);
   Vtransient_mark_mode = Qnil;
 
   DEFVAR_LISP ("inhibit-read-only", &Vinhibit_read_only,