diff --git a/Transceiver52M/ms/ms.cpp b/Transceiver52M/ms/ms.cpp
index ca41144f..b8710a6f 100644
--- a/Transceiver52M/ms/ms.cpp
+++ b/Transceiver52M/ms/ms.cpp
@@ -130,7 +130,7 @@ void ms_trx::submit_burst(blade_sample_type *buffer, int len, GSM::Time target)
 		tosend.decTN(-diff_tn);
 
 	// in theory fn equal and tn+3 equal is also a problem...
-	if (diff_fn < 0 || (diff_fn == 0 && (now_time.TN() - target_tn < 1))) {
+	if (diff_fn < 0 || (diff_fn == 0 && (target_tn-now_time.TN() < 3))) {
 		std::cerr << "## TX too late?! fn DIFF:" << diff_fn << " tn LOCAL: " << now_time.TN()
 			  << " tn OTHER: " << target_tn << std::endl;
 		return;
diff --git a/Transceiver52M/ms/ms_upper.cpp b/Transceiver52M/ms/ms_upper.cpp
index 63c222f2..db15226f 100644
--- a/Transceiver52M/ms/ms_upper.cpp
+++ b/Transceiver52M/ms/ms_upper.cpp
@@ -258,6 +258,7 @@ void upper_trx::driveReceiveFIFO()
 		trxcon_phyif_handle_burst_ind(g_trxcon, &bi);
 	}
 
+	burstTime.incTN(2);
 	struct trxcon_phyif_rts_ind rts {
 		static_cast<uint32_t>(burstTime.FN()), static_cast<uint8_t>(burstTime.TN())
 	};