diff --git a/src/engine/platform/sms.cpp b/src/engine/platform/sms.cpp
index 325665003..114d67b05 100644
--- a/src/engine/platform/sms.cpp
+++ b/src/engine/platform/sms.cpp
@@ -301,7 +301,9 @@ void DivPlatformSMS::poke(std::vector<DivRegWrite>& wlist) {
 }
 
 void DivPlatformSMS::setFlags(unsigned int flags) {
-  if ((flags&3)==2) {
+  if ((flags&3)==3) {
+    chipClock=COLOR_NTSC/2.0;
+  } else if ((flags&3)==2) {
     chipClock=4000000;
   } else if ((flags&3)==1) {
     chipClock=COLOR_PAL*4.0/5.0;
diff --git a/src/gui/gui.cpp b/src/gui/gui.cpp
index 10a7159c2..1a5a13f47 100644
--- a/src/gui/gui.cpp
+++ b/src/gui/gui.cpp
@@ -4544,6 +4544,10 @@ bool FurnaceGUI::loop() {
                   e->setSysFlags(i,(flags&(~3))|2,restart);
                   updateWindowTitle();
                 }
+                if (ImGui::RadioButton("Half NTSC (1.79MHz)",(flags&3)==3)) {
+                  e->setSysFlags(i,(flags&(~3))|3,restart);
+                  updateWindowTitle();
+                }
                 ImGui::Text("Chip type:");
                 if (ImGui::RadioButton("Sega VDP/Master System",((flags>>2)&3)==0)) {
                   e->setSysFlags(i,(flags&(~12))|0,restart);