diff --git a/src/engine/platform/sms.cpp b/src/engine/platform/sms.cpp
index d22316865..af7629ecd 100644
--- a/src/engine/platform/sms.cpp
+++ b/src/engine/platform/sms.cpp
@@ -211,6 +211,7 @@ void DivPlatformSMS::forceIns() {
       chan[i].freqChanged=true;
     }
   }
+  updateSNMode=true;
 }
 
 void* DivPlatformSMS::getChanState(int ch) {
diff --git a/src/engine/song.h b/src/engine/song.h
index cd9c460d8..ab8c7daf9 100644
--- a/src/engine/song.h
+++ b/src/engine/song.h
@@ -136,11 +136,13 @@ struct DivSong {
   //     - 0: NTSC (3.58MHz)
   //     - 1: PAL (3.55MHz)
   //     - 2: Other (4MHz)
+  //     - 3: half NTSC (1.79MHz)
   //   - bit 2-3: noise type
   //     - 0: Sega VDP (16-bit noise)
   //     - 1: real SN76489 (15-bit noise)
   //     - 2: real SN76489 with Atari-like short noise buzz (15-bit noise)
   //     - 3: Game Gear (16-bit noise, stereo)
+  //   - bit 4: disable noise phase reset
   // - YM2612:
   //   - bit 0-1: clock rate
   //     - 0: Genesis NTSC (7.67MHz)
diff --git a/src/gui/gui.cpp b/src/gui/gui.cpp
index 35bf2f81b..0fcb8c55b 100644
--- a/src/gui/gui.cpp
+++ b/src/gui/gui.cpp
@@ -5688,7 +5688,7 @@ bool FurnaceGUI::loop() {
                 }
                 break;
               }
-              case DIV_SYSTEM_SMS:
+              case DIV_SYSTEM_SMS: {
                 ImGui::Text("Clock rate:");
                 if (ImGui::RadioButton("NTSC (3.58MHz)",(flags&3)==0)) {
                   e->setSysFlags(i,(flags&(~3))|0,restart);
@@ -5700,19 +5700,25 @@ bool FurnaceGUI::loop() {
                   e->setSysFlags(i,(flags&(~3))|2,restart);
                 }
                 ImGui::Text("Chip type:");
-                if (ImGui::RadioButton("Sega VDP/Master System",(flags>>2)==0)) {
-                  e->setSysFlags(i,(flags&3)|0,restart);
+                if (ImGui::RadioButton("Sega VDP/Master System",((flags>>2)&3)==0)) {
+                  e->setSysFlags(i,(flags&(~12))|0,restart);
                 }
-                if (ImGui::RadioButton("TI SN76489",(flags>>2)==1)) {
-                  e->setSysFlags(i,(flags&3)|4,restart);
+                if (ImGui::RadioButton("TI SN76489",((flags>>2)&3)==1)) {
+                  e->setSysFlags(i,(flags&(~12))|4,restart);
                 }
-                if (ImGui::RadioButton("TI SN76489 with Atari-like short noise",(flags>>2)==2)) {
-                  e->setSysFlags(i,(flags&3)|8,restart);
+                if (ImGui::RadioButton("TI SN76489 with Atari-like short noise",((flags>>2)&3)==2)) {
+                  e->setSysFlags(i,(flags&(~12))|8,restart);
                 }
                 /*if (ImGui::RadioButton("Game Gear",(flags>>2)==3)) {
                   e->setSysFlags(i,(flags&3)|12);
                 }*/
+
+                bool noPhaseReset=flags&16;
+                if (ImGui::Checkbox("Disable noise period change phase reset",&noPhaseReset)) {
+                  e->setSysFlags(i,(flags&(~16))|(noPhaseReset<<4),restart);
+                }
                 break;
+              }
               case DIV_SYSTEM_ARCADE:
               case DIV_SYSTEM_YM2151:
                 if (ImGui::RadioButton("NTSC (3.58MHz)",flags==0)) {