diff -urN rt_v61/cross.c rt_v62/cross.c
--- rt_v61/cross.c	2018-07-13 20:09:46.000000000 +0900
+++ rt_v62/cross.c	2018-07-14 13:00:38.000000000 +0900
@@ -349,6 +349,12 @@
 
 		v_add(x, ret->p, x);
 		v_add(z, ret->p, z);
+
+		if( v_eq(x, ret->p) || v_eq(z, ret->p) ){
+			ret->ang_nv_eyev = 0;		
+			return;
+		}
+
 		lstx_tr_p(l2g, L2G, x, x);
 		lstx_tr_p(l2g, L2G, z, z);
 		v_sub(x, p, x);
@@ -559,6 +565,9 @@
 	if( ret->idx >= 0 ){
 		struct data_one *d = &data->lst[ ret->idx ];
 		cross_get_nv( d->kind, &d->l2g, l_g, d->not, ret );
+		if( ret->ang_nv_eyev == 0 ){
+			ret->idx = -1;
+		}
 	}
 }