diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 251315c35747..ff3286fc22d8 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -1312,6 +1312,11 @@ static void csi_m(struct vc_data *vc)
 			case 3:
 				vc->vc_italic = 1;
 				break;
+			case 21:
+				/*
+				 * No console drivers support double underline, so
+				 * convert it to a single underline.
+				 */
 			case 4:
 				vc->vc_underline = 1;
 				break;
@@ -1348,7 +1353,6 @@ static void csi_m(struct vc_data *vc)
 				vc->vc_disp_ctrl = 1;
 				vc->vc_toggle_meta = 1;
 				break;
-			case 21:
 			case 22:
 				vc->vc_intensity = 1;
 				break;