diff --git a/debug.c b/debug.c
index 9a02266..3e76ae6 100644
--- a/debug.c
+++ b/debug.c
@@ -1299,10 +1299,11 @@ do_set_var(CMDARG *arg, int cmd ATTRIBUTE_UNUSED)
 		arg = arg->next;
 		val = arg->a_node;
 		lhs = get_field(field_num, &assign);
-		unref(*lhs);
-		*lhs = dupnode(val);
 		if (assign)
+			/* call assign to copy fields before unref frees $0 */
 			assign();
+		unref(*lhs);
+		*lhs = dupnode(val);
 		print_field(field_num);
 	}
 		break;