--- a/src/yapf/yapf_costrail.hpp	Mon Jul 09 16:32:52 2007 +0000
+++ b/src/yapf/yapf_costrail.hpp	Mon Jul 09 18:27:42 2007 +0000
@@ -376,6 +376,7 @@
 			tf_local.Init(v, &Yapf().m_perf_ts_cost);
 
 			if (!tf_local.Follow(cur.tile, cur.td)) {
+				assert(tf_local.m_err != TrackFollower::EC_NONE);
 				/* Can't move to the next tile (EOL?). */
 				end_segment_reason |= ESRB_DEAD_END;
 				break;