diff --git a/ares/component/processor/m68000/m68000.cpp b/ares/component/processor/m68000/m68000.cpp
index be752caf34..cd61184ef3 100644
--- a/ares/component/processor/m68000/m68000.cpp
+++ b/ares/component/processor/m68000/m68000.cpp
@@ -66,7 +66,7 @@ auto M68000::exception(u32 exception, u32 vector, u32 priority) -> void {
   if(exception == Exception::Interrupt) {
     // IACK vector number acquisition (+4 cyc normal or +10 to +18 cyc autovectored)
     // & justify vector number (+4 cyc)
-    idle(16+4); // assuming autovector cycles (approximated for Megadrive)
+    idle(14+4); // assuming autovector cycles (approximated for Megadrive)
     r.i = priority;
   }
 
diff --git a/ares/md/apu/bus.cpp b/ares/md/apu/bus.cpp
index 27497ffb1c..783e988260 100644
--- a/ares/md/apu/bus.cpp
+++ b/ares/md/apu/bus.cpp
@@ -33,7 +33,9 @@ auto APU::write(n16 address, n8 data) -> void {
 }
 
 auto APU::readExternal(n24 address) -> n8 {
+  step(3); // approximate Z80 delay
   while(MegaDrive::bus.acquired() && !scheduler.synchronizing()) step(1);
+  cpu.state.stolenMcycles += 68; // approximate 68K delay; 68 Mclk ~= 9.7 68k clk
   MegaDrive::bus.acquire(MegaDrive::Bus::APU);
 
   n8 data = 0xff;
@@ -54,7 +56,9 @@ auto APU::readExternal(n24 address) -> n8 {
 }
 
 auto APU::writeExternal(n24 address, n8 data) -> void {
+  step(3); // approximate Z80 delay
   while(MegaDrive::bus.acquired() && !scheduler.synchronizing()) step(1);
+  cpu.state.stolenMcycles += 68; // approximate 68K delay; 68 Mclk ~= 9.7 68k clk
   MegaDrive::bus.acquire(MegaDrive::Bus::APU);
 
   if(address >= 0x000000 && address <= 0x9fffff
diff --git a/ares/md/bus/inline.hpp b/ares/md/bus/inline.hpp
index d97fb31352..94ca812ee6 100644
--- a/ares/md/bus/inline.hpp
+++ b/ares/md/bus/inline.hpp
@@ -121,47 +121,31 @@ alwaysinline auto Bus::write(n1 upper, n1 lower, n24 address, n16 data) -> void
 }
 
 alwaysinline auto Bus::waitRefreshExternal() -> void {
-  if(state.acquired & VDPDMA) return; // refresh is synched with VDP during DMA
-  if(cpu.refresh.external < cpu.refresh.externalLowBound) return;
-
-  if(cpu.refresh.externalEnd == 0)
-    cpu.refresh.externalEnd = min(cpu.refresh.external + cpu.refresh.externalLength, cpu.refresh.externalHighBound);
-  if(cpu.refresh.external < cpu.refresh.externalEnd) {
-    while(cpu.refresh.external < cpu.refresh.externalEnd) {
-      if(cpu.active()) cpu.wait(1);
-      if(apu.active()) apu.step(1);
-      if(scheduler.synchronizing()) return;
-      if(vdp.active()) return;
-    }
-    cpu.refresh.external -= cpu.refresh.externalEnd;
-    cpu.refresh.externalEnd = 0;
-  }
+  if(vdp.active() || state.acquired & VDPDMA) return; // refresh is synched with VDP during DMA
 
   while(cpu.refresh.external >= cpu.refresh.externalHighBound) {
     cpu.refresh.external -= cpu.refresh.externalHighBound;
-    cpu.refresh.externalEnd = 0;
   }
+
+  if(cpu.refresh.external < cpu.refresh.externalLowBound) return;
+
+  if(cpu.active()) cpu.wait(min(cpu.refresh.externalLength,cpu.refresh.externalHighBound-cpu.refresh.external));
+  if(apu.active()) apu.step(min(cpu.refresh.externalLength,cpu.refresh.externalHighBound-cpu.refresh.external));
+
+  cpu.refresh.external -= cpu.refresh.externalHighBound;
 }
 
 alwaysinline auto Bus::waitRefreshRAM() -> void {
-  if(state.acquired & VDPDMA) return; // refresh is synched with VDP during DMA
-  if(cpu.refresh.ram < cpu.refresh.ramLowBound) return;
-
-  if(cpu.refresh.ramEnd == 0)
-    cpu.refresh.ramEnd = min(cpu.refresh.ram + cpu.refresh.ramLength, cpu.refresh.ramHighBound);
-  if(cpu.refresh.ram < cpu.refresh.ramEnd) {
-    while(cpu.refresh.ram < cpu.refresh.ramEnd) {
-      if(cpu.active()) cpu.wait(1);
-      if(apu.active()) apu.step(1);
-      if(scheduler.synchronizing()) return;
-      if(vdp.active()) return;
-    }
-    cpu.refresh.ram -= cpu.refresh.ramEnd;
-    cpu.refresh.ramEnd = 0;
-  }
+  if(vdp.active() || state.acquired & VDPDMA) return; // refresh is synched with VDP during DMA
 
   while(cpu.refresh.ram >= cpu.refresh.ramHighBound) {
     cpu.refresh.ram -= cpu.refresh.ramHighBound;
-    cpu.refresh.ramEnd = 0;
   }
+
+  if(cpu.refresh.ram < cpu.refresh.ramLowBound) return;
+
+  if(cpu.active()) cpu.wait(min(cpu.refresh.ramLength,cpu.refresh.ramHighBound-cpu.refresh.ram));
+  if(apu.active()) apu.step(min(cpu.refresh.ramLength,cpu.refresh.ramHighBound-cpu.refresh.ram));
+
+  cpu.refresh.ram = 0;
 }
diff --git a/ares/md/cpu/cpu.cpp b/ares/md/cpu/cpu.cpp
index e5fe5af5c2..ae5754f65a 100644
--- a/ares/md/cpu/cpu.cpp
+++ b/ares/md/cpu/cpu.cpp
@@ -60,6 +60,8 @@ auto CPU::main() -> void {
 }
 
 auto CPU::step(u32 clocks) -> void {
+  clocks += state.stolenMcycles/7;
+  state.stolenMcycles -= state.stolenMcycles/7 * 7;
   refresh.ram += clocks;
   refresh.external += clocks;
   Thread::step(clocks);
diff --git a/ares/md/cpu/cpu.hpp b/ares/md/cpu/cpu.hpp
index 1a59cc7a6f..6cd0b16801 100644
--- a/ares/md/cpu/cpu.hpp
+++ b/ares/md/cpu/cpu.hpp
@@ -74,14 +74,15 @@ struct CPU : M68000, Thread {
     static constexpr int ramLowBound       = 113;
     static constexpr int ramHighBound      = 132;
     static constexpr int ramLength         = 3;
-    static constexpr int externalLowBound  = 126;
-    static constexpr int externalHighBound = 132;
+    static constexpr int externalLowBound  = 121;
+    static constexpr int externalHighBound = 128;
     static constexpr int externalLength    = 2;
 
   } refresh;
 
   struct State {
     n32 interruptPending;
+    int stolenMcycles = 0;
   } state;
 
   int cyclesUntilSync = 0;
diff --git a/ares/md/cpu/serialization.cpp b/ares/md/cpu/serialization.cpp
index fc90841d36..9bb2dea161 100644
--- a/ares/md/cpu/serialization.cpp
+++ b/ares/md/cpu/serialization.cpp
@@ -10,4 +10,5 @@ auto CPU::serialize(serializer& s) -> void {
   s(refresh.external);
   s(refresh.externalEnd);
   s(state.interruptPending);
+  s(state.stolenMcycles);
 }
diff --git a/ares/md/system/serialization.cpp b/ares/md/system/serialization.cpp
index 9959c160f4..21efa43191 100644
--- a/ares/md/system/serialization.cpp
+++ b/ares/md/system/serialization.cpp
@@ -1,4 +1,4 @@
-static const string SerializerVersion = "v133";
+static const string SerializerVersion = "v133.1";
 
 auto System::serialize(bool synchronize) -> serializer {
   if(synchronize) scheduler.enter(Scheduler::Mode::Synchronize);