Index: trunk/src_plugins/sketch_route/spoke.c
===================================================================
--- trunk/src_plugins/sketch_route/spoke.c	(revision 18477)
+++ trunk/src_plugins/sketch_route/spoke.c	(revision 18478)
@@ -89,6 +89,8 @@
 	pcb_coord_t spacing = 0;
 	int i;
 
+	assert(slot < vtp0_len(&sp->slots));
+
 	for (i = 0; i < slot; i++) {
 		spacing += conf_core.design.bloat;
 		spacing += ((ewire_t *) (sp->slots.array[i]))->wire->thickness;