Index: layer_vis.c
===================================================================
--- layer_vis.c	(revision 18338)
+++ layer_vis.c	(revision 18339)
@@ -85,12 +85,12 @@
 
 
 	if (Layer & PCB_LYT_UI) {
+		pcb_layer_t *ly = pcb_uilayer_get(Layer);
+		if (ly == NULL)
+			return 0;
 		if (On < 0)
-			On = !pcb_uilayer.array[Layer].meta.real.vis;
-		Layer &= ~(PCB_LYT_UI | PCB_LYT_VIRTUAL);
-		if (Layer >= vtlayer_len(&pcb_uilayer))
-			return 0;
-		pcb_uilayer.array[Layer].meta.real.vis = On;
+			On = !ly->meta.real.vis;
+		ly->meta.real.vis = On;
 		changed = 1;
 		goto done;
 	}