diff --git a/channels/misdn/isdn_lib.c b/channels/misdn/isdn_lib.c
index 8cd2fd10f1..835f75cf66 100644
--- a/channels/misdn/isdn_lib.c
+++ b/channels/misdn/isdn_lib.c
@@ -884,9 +884,10 @@ static int misdn_lib_get_l2_down(struct misdn_stack *stack)
 		/* L2 */
 		dmsg = create_l2msg(DL_RELEASE| REQUEST, 0, 0);
 
+		pthread_mutex_lock(&stack->nstlock);
 		if (stack->nst.manager_l3(&stack->nst, dmsg))
 			free_msg(dmsg);
-
+		pthread_mutex_unlock(&stack->nstlock);
 	} else {
 		iframe_t act;
 
@@ -925,9 +926,10 @@ int misdn_lib_get_l2_up(struct misdn_stack *stack)
 		/* L2 */
 		dmsg = create_l2msg(DL_ESTABLISH | REQUEST, 0, 0);
 
+		pthread_mutex_lock(&stack->nstlock);
 		if (stack->nst.manager_l3(&stack->nst, dmsg))
 			free_msg(dmsg);
-
+		pthread_mutex_unlock(&stack->nstlock);
 	} else {
 		iframe_t act;
 
@@ -1427,6 +1429,7 @@ static struct misdn_stack *stack_init(int midev, int port, int ptp)
 			stack->nst.l2_id = stack->upper_id;
 
 			msg_queue_init(&stack->nst.down_queue);
+			pthread_mutex_init(&stack->nstlock, NULL);
 
 			Isdnl2Init(&stack->nst);
 			Isdnl3Init(&stack->nst);
@@ -1463,6 +1466,7 @@ static void stack_destroy(struct misdn_stack *stack)
 	if (!stack) return;
 
 	if (stack->nt) {
+		pthread_mutex_destroy(&stack->nstlock);
 		cleanup_Isdnl2(&stack->nst);
 		cleanup_Isdnl3(&stack->nst);
 	}
@@ -1936,7 +1940,6 @@ static int handle_event_nt(void *dat, void *arg)
 	struct misdn_stack *stack;
 	enum event_e event;
 	int reject=0;
-	int port;
 	int l3id;
 	int channel;
 	int tmpcause;
@@ -1946,7 +1949,13 @@ static int handle_event_nt(void *dat, void *arg)
 
 	stack = find_stack_by_mgr(mgr);
 	hh=(mISDNuser_head_t*)msg->data;
-	port=stack->port;
+
+	/*
+	 * When we are called from the mISDNuser lib, the nstlock is held and it
+	 * must be held when we return.  We unlock here because the lib may be
+	 * entered again recursively.
+	 */
+	pthread_mutex_unlock(&stack->nstlock);
 
 	cb_log(5, stack->port, " --> lib: prim %x dinfo %x\n",hh->prim, hh->dinfo);
 	switch(hh->prim) {
@@ -1994,6 +2003,7 @@ static int handle_event_nt(void *dat, void *arg)
 			cb_log(4, stack->port, "Bc Not found (after SETUP CONFIRM)\n");
 		}
 		free_msg(msg);
+		pthread_mutex_lock(&stack->nstlock);
 		return 0;
 
 	case CC_SETUP | INDICATION:
@@ -2020,6 +2030,7 @@ static int handle_event_nt(void *dat, void *arg)
 			cb_log(4, stack->port, "Bc Not found (after REGISTER CONFIRM)\n");
 		}
 		free_msg(msg);
+		pthread_mutex_lock(&stack->nstlock);
 		return 0;
 #endif	/* defined(AST_MISDN_ENHANCEMENTS) */
 
@@ -2076,6 +2087,7 @@ static int handle_event_nt(void *dat, void *arg)
 	case CC_SUSPEND|INDICATION:
 		cb_log(4, stack->port, " --> Got Suspend, sending Reject for now\n");
 		dmsg = create_l3msg(CC_SUSPEND_REJECT | REQUEST,MT_SUSPEND_REJECT, hh->dinfo,sizeof(RELEASE_COMPLETE_t), 1);
+		pthread_mutex_lock(&stack->nstlock);
 		stack->nst.manager_l3(&stack->nst, dmsg);
 		free_msg(msg);
 		return 0;
@@ -2097,6 +2109,7 @@ static int handle_event_nt(void *dat, void *arg)
 	case CC_RELEASE_CR|INDICATION:
 		release_cr(stack, hh);
 		free_msg(msg);
+		pthread_mutex_lock(&stack->nstlock);
 		return 0;
 
 	case CC_NEW_CR|INDICATION:
@@ -2107,6 +2120,7 @@ static int handle_event_nt(void *dat, void *arg)
 		bc = find_bc_by_l3id(stack, hh->dinfo);
 		if (!bc) {
 			cb_log(0, stack->port, " --> In NEW_CR: didn't found bc ??\n");
+			pthread_mutex_lock(&stack->nstlock);
 			return -1;
 		}
 		if (((l3id&0xff00)!=0xff00) && ((bc->l3_id&0xff00)==0xff00)) {
@@ -2121,6 +2135,7 @@ static int handle_event_nt(void *dat, void *arg)
 		}
 
 		free_msg(msg);
+		pthread_mutex_lock(&stack->nstlock);
 		return 0;
 
 	case DL_ESTABLISH | INDICATION:
@@ -2145,6 +2160,7 @@ static int handle_event_nt(void *dat, void *arg)
 		stack->l2upcnt=0;
 
 		free_msg(msg);
+		pthread_mutex_lock(&stack->nstlock);
 		return 0;
 
 	case DL_RELEASE | INDICATION:
@@ -2170,6 +2186,7 @@ static int handle_event_nt(void *dat, void *arg)
 
 		stack->l2link = 0;
 		free_msg(msg);
+		pthread_mutex_lock(&stack->nstlock);
 		return 0;
 
 	default:
@@ -2231,11 +2248,13 @@ static int handle_event_nt(void *dat, void *arg)
 	}
 
 	free_msg(msg);
+	pthread_mutex_lock(&stack->nstlock);
 	return 0;
 
 ERR_NO_CHANNEL:
 	cb_log(4, stack->port, "Patch from MEIDANIS:Sending RELEASE_COMPLETE %x (No free Chan for you..)\n", hh->dinfo);
 	dmsg = create_l3msg(CC_RELEASE_COMPLETE | REQUEST, MT_RELEASE_COMPLETE, hh->dinfo, sizeof(RELEASE_COMPLETE_t), 1);
+	pthread_mutex_lock(&stack->nstlock);
 	stack->nst.manager_l3(&stack->nst, dmsg);
 	free_msg(msg);
 	return 0;
@@ -2280,7 +2299,9 @@ static int handle_timers(msg_t* msg)
 				ret = mISDN_write_frame(stack->midev, msg->data, frm->addr,
 							MGR_TIMER | RESPONSE, 0, 0, NULL, TIMEOUT_1SEC);
 				test_and_clear_bit(FLG_TIMER_RUNING, (long unsigned int *)&it->Flags);
+				pthread_mutex_lock(&stack->nstlock);
 				ret = it->function(it->data);
+				pthread_mutex_unlock(&stack->nstlock);
 				free_msg(msg);
 				return 1;
 			}
@@ -2703,8 +2724,9 @@ static int handle_frm_nt(msg_t *msg)
 	}
 
 
+	pthread_mutex_lock(&stack->nstlock);
 	if ((err=stack->nst.l1_l2(&stack->nst,msg))) {
-
+		pthread_mutex_unlock(&stack->nstlock);
 		if (nt_err_cnt > 0 ) {
 			if (nt_err_cnt < 100) {
 				nt_err_cnt++;
@@ -2716,9 +2738,8 @@ static int handle_frm_nt(msg_t *msg)
 		}
 		free_msg(msg);
 		return 1;
-
 	}
-
+	pthread_mutex_unlock(&stack->nstlock);
 	return 1;
 }
 
@@ -2882,8 +2903,10 @@ static int handle_l1(msg_t *msg)
 
 		if (stack->nt) {
 
+			pthread_mutex_lock(&stack->nstlock);
 			if (stack->nst.l1_l2(&stack->nst, msg))
 				free_msg(msg);
+			pthread_mutex_unlock(&stack->nstlock);
 
 			if (stack->ptp)
 				misdn_lib_get_l2_up(stack);
@@ -2924,8 +2947,10 @@ static int handle_l1(msg_t *msg)
 #endif
 
 		if (stack->nt) {
+			pthread_mutex_lock(&stack->nstlock);
 			if (stack->nst.l1_l2(&stack->nst, msg))
 				free_msg(msg);
+			pthread_mutex_unlock(&stack->nstlock);
 		} else {
 			free_msg(msg);
 		}
@@ -3014,16 +3039,16 @@ static int handle_mgmt(msg_t *msg)
 	switch(frm->prim) {
 	case MGR_SHORTSTATUS | INDICATION:
 	case MGR_SHORTSTATUS | CONFIRM:
-		cb_log(5, 0, "MGMT: Short status dinfo %x\n",frm->dinfo);
+		cb_log(5, stack->port, "MGMT: Short status dinfo %x\n",frm->dinfo);
 
 		switch (frm->dinfo) {
 		case SSTATUS_L1_ACTIVATED:
-			cb_log(3, 0, "MGMT: SSTATUS: L1_ACTIVATED \n");
+			cb_log(3, stack->port, "MGMT: SSTATUS: L1_ACTIVATED \n");
 			stack->l1link=1;
 
 			break;
 		case SSTATUS_L1_DEACTIVATED:
-			cb_log(3, 0, "MGMT: SSTATUS: L1_DEACTIVATED \n");
+			cb_log(3, stack->port, "MGMT: SSTATUS: L1_DEACTIVATED \n");
 			stack->l1link=0;
 #if 0
 			clear_l3(stack);
@@ -4216,9 +4241,10 @@ static void manager_event_handler(void *arg)
 
 			while ( (msg=msg_dequeue(&stack->downqueue)) ) {
 				if (stack->nt ) {
+					pthread_mutex_lock(&stack->nstlock);
 					if (stack->nst.manager_l3(&stack->nst, msg))
 						cb_log(0, stack->port, "Error@ Sending Message in NT-Stack.\n");
-
+					pthread_mutex_unlock(&stack->nstlock);
 				} else {
 					iframe_t *frm = (iframe_t *)msg->data;
 					struct misdn_bchannel *bc = find_bc_by_l3id(stack, frm->dinfo);
diff --git a/channels/misdn/isdn_lib_intern.h b/channels/misdn/isdn_lib_intern.h
index 7e7ea8a614..3d0fd5428a 100644
--- a/channels/misdn/isdn_lib_intern.h
+++ b/channels/misdn/isdn_lib_intern.h
@@ -65,6 +65,7 @@ struct misdn_stack {
 	/** is first element because &nst equals &mISDNlist **/
 	net_stack_t nst;
 	manager_t mgr;
+	pthread_mutex_t nstlock;
 
 	/*! \brief D Channel mISDN driver stack ID (Parent stack ID) */
 	int d_stid;