diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 385f0bbfe..52e70cca5 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -3593,6 +3593,14 @@ A jump table for the options with a short description can be found at |Q_op|.
 	font names a list can be specified, font names separated with commas.
 	The first valid font is used.
 
+	Note: As to the GTK GUIs, no error is given against any invalid names,
+	and the first element of the list is always picked up and made use of.
+	This is because, instead of identifying a given name with a font, the
+	GTK GUIs use it to construct a pattern and try to look up a font which
+	best matches the pattern among available fonts, and this way, the
+	matching never fails.  An invalid name doesn't matter because a number
+	of font properties other than name will do to get the matching done.
+
 	On systems where 'guifontset' is supported (X11) and 'guifontset' is
 	not empty, then 'guifont' is not used.