diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 9fa2bfb..4890a98 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -856,6 +856,8 @@
 		:set background&
 <	Vim will guess the value.  In the GUI this should work correctly,
 	in other cases Vim might not be able to guess the right value.
+	If the GUI supports a dark them, you can use the "d" flag in
+	'guioptions', see 'go-d'.
 
 	When the |t_RB| option is set, Vim will use it to request the background
 	color from the terminal.  If the returned RGB value is dark/light and
@@ -3740,6 +3742,9 @@
 								*'go-c'*
 	  'c'	Use console dialogs instead of popup dialogs for simple
 		choices.
+								*'go-d'*
+	  'd'	Use dark theme variant if available. Currently only works for
+		GTK+ GUI.
 								*'go-e'*
 	  'e'	Add tab pages when indicated with 'showtabline'.
 		'guitablabel' can be used to change the text in the labels.