diff --git a/library/NS_Emulation.ttcnpp b/library/NS_Emulation.ttcnpp
index ab1c13676..2ccd39995 100644
--- a/library/NS_Emulation.ttcnpp
+++ b/library/NS_Emulation.ttcnpp
@@ -561,6 +561,9 @@ module NS_Emulation {
 			Tns_block.stop;
 			f_change_state(NSVC_S_ALIVE_UNBLOCKED);
 		}
+		/* tolerate a late NS-BLOCK-ACK from peer */
+		[] NSCP.receive(tr_NS_BLOCK_ACK(g_nsvc_config.nsvci)) -> value rf {
+		}
 		[] Tns_block.timeout {
 			/* repeat unblock transmission */
 			f_sendUnblock();
@@ -583,6 +586,9 @@ module NS_Emulation {
 		[] NSCP.receive(tr_NS_BLOCK_ACK(g_nsvc_config.nsvci)) -> value rf {
 			Tns_block.stop;
 		}
+		/* tolerate a late NS-UNBLOCK-ACK from peer */
+		[] NSCP.receive(t_NS_UNBLOCK_ACK) -> value rf {
+		}
 		/* NS-UNITDATA PDU from network to NS-UNITDATA.ind to user */
 		[] NSCP.receive(tr_NS_UNITDATA(?, ?, ?)) -> value rf {
 			NS_SP.send(ts_NsUdInd(g_config.nsei, g_nsvc_config.nsvci,