kc3-lang/kc3

diff --git a/ekc3/ekc3.c b/ekc3/ekc3.c
index 5f99803..dea67d9 100644
--- a/ekc3/ekc3.c
+++ b/ekc3/ekc3.c
@@ -424,8 +424,11 @@ sw ekc3_render (s_buf *buf, const p_ekc3 *ekc3)
       }
     }
     else {
-      if (! (r = ekc3_render_tag(buf, &l->tag)))
+      if ((r = ekc3_render_tag(buf, &l->tag)) < 0) {
+        err_puts("ekc3_render: ekc3_render_tag");
+        assert(! "ekc3_render: ekc3_render_tag");
         return r;
+      }
       result += r;
     }
     l = list_next(l);