diff --git a/openflow_input/bsn_pdu b/openflow_input/bsn_pdu
index 0bf29cb..505f8fb 100644
--- a/openflow_input/bsn_pdu
+++ b/openflow_input/bsn_pdu
@@ -59,8 +59,9 @@
     uint32_t xid;
     uint32_t experimenter == 0x5c16c7;
     uint32_t subtype == 33;
-    uint32_t pdu_timeout_ms;
     of_port_no_t port_no;
+    uint16_t is_pdu_expected; // following fields are valid only if this is 1
+    uint32_t pdu_timeout_ms;
     of_octets_t pdu_payload;
 };