Index: layer_vis.h
===================================================================
--- layer_vis.h	(revision 8629)
+++ layer_vis.h	(revision 8630)
@@ -33,8 +33,8 @@
 #include "layer.h"
 
 /* changes the visibility of all layers in a group; returns the number of
-   changed layers */
-int pcb_layervis_change_group_vis(pcb_layer_id_t Layer, pcb_bool On, pcb_bool ChangeStackOrder);
+   changed layers; on should be 0 or 1 for setting the state or -1 for toggling it */
+int pcb_layervis_change_group_vis(pcb_layer_id_t Layer, int On, pcb_bool ChangeStackOrder);
 
 /* resets the layer visibility stack setting */
 void pcb_layervis_reset_stack(void);