diff -Naur pjproject-2.5.5-orig/pjsip/src/pjsip/sip_transport.c pjproject-2.5.5/pjsip/src/pjsip/sip_transport.c
--- pjproject-2.5.5-orig/pjsip/src/pjsip/sip_transport.c	2016-02-25 04:38:34.000000000 +0000
+++ pjproject-2.5.5/pjsip/src/pjsip/sip_transport.c	2016-10-13 13:34:47.838265748 +0000
@@ -461,12 +461,15 @@
  */
 PJ_DEF(void) pjsip_tx_data_add_ref( pjsip_tx_data *tdata )
 {
-    pj_atomic_inc(tdata->ref_cnt);
+    pj_atomic_value_t ref_cnt;
+    ref_cnt = pj_atomic_inc_and_get(tdata->ref_cnt);
+    PJ_LOG(3,(THIS_FILE, "Add ref pjsip_tx_data: %p ref_cnt: %d",
+	      tdata, (int)ref_cnt));
 }
 
 static void tx_data_destroy(pjsip_tx_data *tdata)
 {
-    PJ_LOG(5,(tdata->obj_name, "Destroying txdata %s",
+    PJ_LOG(3,(tdata->obj_name, "Destroying txdata %s",
 	      pjsip_tx_data_get_info(tdata)));
     pjsip_tpselector_dec_ref(&tdata->tp_sel);
 #if defined(PJ_DEBUG) && PJ_DEBUG!=0
@@ -491,11 +494,20 @@
  */
 PJ_DEF(pj_status_t) pjsip_tx_data_dec_ref( pjsip_tx_data *tdata )
 {
-    pj_assert( pj_atomic_get(tdata->ref_cnt) > 0);
-    if (pj_atomic_dec_and_get(tdata->ref_cnt) <= 0) {
+    pj_atomic_value_t ref_cnt;
+    
+    PJ_ASSERT_RETURN(tdata && tdata->ref_cnt, PJ_EINVAL);
+
+    ref_cnt = pj_atomic_dec_and_get(tdata->ref_cnt);
+    pj_assert( ref_cnt >= 0);
+    if (ref_cnt == 0) {
+	PJ_LOG(3,(THIS_FILE, "Destroying pjsip_tx_data: %p",
+		  tdata));
 	tx_data_destroy(tdata);
 	return PJSIP_EBUFDESTROYED;
     } else {
+	PJ_LOG(3,(THIS_FILE, "Dec ref pjsip_tx_data: %p ref_cnt: %d",
+		  tdata, (int)ref_cnt));
 	return PJ_SUCCESS;
     }
 }