diff --git a/src/engine/platform/genesisext.cpp b/src/engine/platform/genesisext.cpp
index d8760be9a..97f52ddac 100644
--- a/src/engine/platform/genesisext.cpp
+++ b/src/engine/platform/genesisext.cpp
@@ -443,13 +443,15 @@ void DivPlatformGenesisExt::muteChannel(int ch, bool mute) {
   DivPlatformGenesis::muteChannel(extChanOffs,IS_EXTCH_MUTED);
   
   if (extMode) {
-    int ordch=orderedOps[ch-2];
-    unsigned short baseAddr=chanOffs[2]|opOffs[ordch];
-    DivInstrumentFM::Operator op=chan[2].state.op[ordch];
-    if (isOpMuted[ch-2] || !op.enable) {
-      rWrite(baseAddr+0x40,127);
-    } else {
-      rWrite(baseAddr+0x40,127-VOL_SCALE_LOG_BROKEN(127-op.tl,opChan[ch-2].outVol&0x7f,127));
+    for (int i=0; i<4; i++) {
+      int ordch=orderedOps[i];
+      unsigned short baseAddr=chanOffs[2]|opOffs[ordch];
+      DivInstrumentFM::Operator op=chan[2].state.op[ordch];
+      if (isOpMuted[i] || !op.enable) {
+        rWrite(baseAddr+0x40,127);
+      } else {
+        rWrite(baseAddr+0x40,127-VOL_SCALE_LOG_BROKEN(127-op.tl,opChan[i].outVol&0x7f,127));
+      }
     }
 
     rWrite(chanOffs[2]+0xb4,(IS_EXTCH_MUTED?0:(opChan[ch-2].pan<<6))|(chan[2].state.fms&7)|((chan[2].state.ams&3)<<4));