diff --git a/libs/freetdm/src/ftmod/ftmod_zt/ftmod_zt.c b/libs/freetdm/src/ftmod/ftmod_zt/ftmod_zt.c
index d9000a6bbb..ae9398418a 100644
--- a/libs/freetdm/src/ftmod/ftmod_zt/ftmod_zt.c
+++ b/libs/freetdm/src/ftmod/ftmod_zt/ftmod_zt.c
@@ -974,7 +974,7 @@ FIO_SPAN_POLL_EVENT_FUNCTION(zt_poll_event)
  */
 FIO_SPAN_NEXT_EVENT_FUNCTION(zt_next_event)
 {
-	uint32_t i, event_id = 0;
+	uint32_t i, event_id = FTDM_OOB_INVALID;
 	zt_event_t zt_event_id = 0;
 
 	for(i = 1; i <= span->chan_count; i++) {
@@ -1022,6 +1022,8 @@ FIO_SPAN_NEXT_EVENT_FUNCTION(zt_next_event)
 						event_id = FTDM_OOB_OFFHOOK;
 					} else if (span->channels[i]->type == FTDM_CHAN_TYPE_FXO) {
 						event_id = FTDM_OOB_RING_START;
+					} else {
+						event_id = FTDM_OOB_NOOP;
 					}
 				}
 				break;
diff --git a/libs/openzap/src/ozmod/ozmod_zt/ozmod_zt.c b/libs/openzap/src/ozmod/ozmod_zt/ozmod_zt.c
index 0eaf955196..ca42c2c578 100644
--- a/libs/openzap/src/ozmod/ozmod_zt/ozmod_zt.c
+++ b/libs/openzap/src/ozmod/ozmod_zt/ozmod_zt.c
@@ -977,7 +977,7 @@ ZIO_SPAN_POLL_EVENT_FUNCTION(zt_poll_event)
  */
 ZIO_SPAN_NEXT_EVENT_FUNCTION(zt_next_event)
 {
-	uint32_t i, event_id = 0;
+	uint32_t i, event_id = ZAP_OOB_INVALID;
 	zt_event_t zt_event_id = 0;
 
 	for(i = 1; i <= span->chan_count; i++) {
@@ -1025,6 +1025,8 @@ ZIO_SPAN_NEXT_EVENT_FUNCTION(zt_next_event)
 						event_id = ZAP_OOB_OFFHOOK;
 					} else if (span->channels[i]->type == ZAP_CHAN_TYPE_FXO) {
 						event_id = ZAP_OOB_RING_START;
+					} else {
+						event_id = ZAP_OOB_NOOP;
 					}
 				}
 				break;