diff --git a/src/engine/platform/ym2610b.cpp b/src/engine/platform/ym2610b.cpp
index f35e7f5bb..634432ace 100644
--- a/src/engine/platform/ym2610b.cpp
+++ b/src/engine/platform/ym2610b.cpp
@@ -1701,7 +1701,7 @@ void DivPlatformYM2610B::muteChannel(int ch, bool mute) {
 }
 
 void DivPlatformYM2610B::forceIns() {
-  for (int i=0; i<psgChanOffs; i++) {
+  for (int i=0; i<(psgChanOffs-isCSM); i++) {
     for (int j=0; j<4; j++) {
       unsigned short baseAddr=chanOffs[i]|opOffs[j];
       DivInstrumentFM::Operator& op=chan[i].state.op[j];
diff --git a/src/engine/platform/ym2610bext.cpp b/src/engine/platform/ym2610bext.cpp
index b01e8407b..d8a986e3c 100644
--- a/src/engine/platform/ym2610bext.cpp
+++ b/src/engine/platform/ym2610bext.cpp
@@ -694,7 +694,7 @@ void DivPlatformYM2610BExt::muteChannel(int ch, bool mute) {
 }
 
 void DivPlatformYM2610BExt::forceIns() {
-  for (int i=0; i<psgChanOffs; i++) {
+  for (int i=0; i<(psgChanOffs-isCSM); i++) {
     for (int j=0; j<4; j++) {
       unsigned short baseAddr=chanOffs[i]|opOffs[j];
       DivInstrumentFM::Operator& op=chan[i].state.op[j];
diff --git a/src/engine/platform/ym2610ext.cpp b/src/engine/platform/ym2610ext.cpp
index 1c789ca58..16f0f02e8 100644
--- a/src/engine/platform/ym2610ext.cpp
+++ b/src/engine/platform/ym2610ext.cpp
@@ -693,7 +693,7 @@ void DivPlatformYM2610Ext::muteChannel(int ch, bool mute) {
 }
 
 void DivPlatformYM2610Ext::forceIns() {
-  for (int i=0; i<psgChanOffs; i++) {
+  for (int i=0; i<(psgChanOffs-isCSM); i++) {
     for (int j=0; j<4; j++) {
       unsigned short baseAddr=chanOffs[i]|opOffs[j];
       DivInstrumentFM::Operator& op=chan[i].state.op[j];