diff --git a/src/vnet/session-apps/echo_server.c b/src/vnet/session-apps/echo_server.c
index f34a490..7d1ae5a 100644
--- a/src/vnet/session-apps/echo_server.c
+++ b/src/vnet/session-apps/echo_server.c
@@ -63,6 +63,8 @@
     session_manager_get_vpp_event_queue (s->thread_index);
   s->session_state = SESSION_STATE_READY;
   esm->byte_index = 0;
+  ASSERT (vec_len (esm->rx_retries) > s->thread_index);
+  vec_validate (esm->rx_retries[s->thread_index], s->session_index);
   esm->rx_retries[s->thread_index][s->session_index] = 0;
   return 0;
 }