diff --git a/src/engine/platform/sms.cpp b/src/engine/platform/sms.cpp
index 258f5434..9d3f32ce 100644
--- a/src/engine/platform/sms.cpp
+++ b/src/engine/platform/sms.cpp
@@ -47,6 +47,7 @@ void DivPlatformSMS::tick() {
   for (int i=0; i<3; i++) {
     if (chan[i].freqChanged) {
       chan[i].freq=parent->calcFreq(chan[i].baseFreq,chan[i].pitch,true);
+      if (chan[i].freq>1023) chan[i].freq=1023;
       if (chan[i].note>0x5d) chan[i].freq=0x01;
       rWrite(0x80|i<<5|(chan[i].freq&15));
       rWrite(chan[i].freq>>4);
@@ -57,6 +58,7 @@ void DivPlatformSMS::tick() {
     updateSNMode=false;
     // seems arbitrary huh?
     chan[3].freq=parent->calcFreq(chan[3].baseFreq,chan[3].pitch-1,true);
+    if (chan[3].freq>1023) chan[3].freq=1023;
     if (chan[3].note>0x5d) chan[3].freq=0x01;
     chan[3].freqChanged=false;
     if (snNoiseMode&2) { // take period from channel 3