diff --git a/linphone/coreapi/callbacks.c b/my_version_to_patch/linphone_with_very_improved_refer/coreapi/callbacks.c
index 5461531..91fa6c2 100644
--- a/linphone/coreapi/callbacks.c
+++ b/my_version_to_patch/linphone_with_very_improved_refer/coreapi/callbacks.c
@@ -396,6 +396,7 @@ static void refer_received(Sal *sal, SalOp *op, const char *referto){
 	LinphoneCore *lc=(LinphoneCore *)sal_get_user_pointer(sal);
 	if(op != NULL)
 	{
+		eXosip_lock();
 		eXosip_call_build_notify(op->tid,EXOSIP_SUBCRSTATE_ACTIVE,&msg);
 		if(msg != NULL)
 		{
@@ -404,6 +405,7 @@ static void refer_received(Sal *sal, SalOp *op, const char *referto){
 			osip_message_set_body(msg,"SIP/2.0 100 Trying",sizeof("SIP/2.0 100 Trying"));
 			eXosip_call_send_request(op->tid,msg);
 		}
+		eXosip_unlock();
 	}
 	if (lc->vtable.refer_received)
 		lc->vtable.refer_received(lc,referto);
diff --git a/linphone/coreapi/sal_eXosip2.c b/my_version_to_patch/linphone_with_very_improved_refer/coreapi/sal_eXosip2.c
index 82bae96..bae7d8b 100644
--- a/linphone/coreapi/sal_eXosip2.c
+++ b/my_version_to_patch/linphone_with_very_improved_refer/coreapi/sal_eXosip2.c
@@ -1099,6 +1099,10 @@ static void call_message_new(Sal *sal, eXosip_event_t *ev){
 				SalOp *op=(SalOp*)ev->external_reference;
 				sal->callbacks.refer_received(sal,op,h->hvalue);
 			}
+			else
+			{
+				ms_warning("cannot do anything with the refer without destination\n");
+			}
 		}
 		if(MSG_IS_NOTIFY(ev->request)){
 			osip_header_t *h=NULL;