Index: trunk/src/libgrbs/collision.c
===================================================================
--- trunk/src/libgrbs/collision.c	(revision 1317)
+++ trunk/src/libgrbs/collision.c	(revision 1318)
@@ -28,7 +28,7 @@
 
 static void coll_report(grbs_t *grbs, grbs_2net_t *tn, grbs_2net_t *coll_tn, grbs_arc_t *coll_arc)
 {
-	if (grbs->coll_report_cb != NULL)
+	if ((grbs->coll_report_cb != NULL) && (coll_tn != NULL))
 		grbs->coll_report_cb(grbs, tn, coll_tn, coll_arc);
 }