diff --git a/source/6522.cpp b/source/6522.cpp
index 8922773d..e375dfc7 100644
--- a/source/6522.cpp
+++ b/source/6522.cpp
@@ -202,6 +202,10 @@ void SY6522::Write(BYTE nReg, BYTE nValue)
 			nValue &= 0x7F;
 			m_regs.IER |= nValue;
 		}
+		if (m_syncEvent[0])
+			m_syncEvent[0]->m_canAssertIRQ = (m_regs.IER & IxR_TIMER1) ? true : false;
+		if (m_syncEvent[1])
+			m_syncEvent[1]->m_canAssertIRQ = (m_regs.IER & IxR_TIMER2) ? true : false;
 		UpdateIFR(0);
 		break;
 	case 0x0f:	// ORA_NO_HS
@@ -669,12 +673,14 @@ void SY6522::SetTimersActiveFromSnapshot(bool timer1Active, bool timer2Active, U
 	{
 		SyncEvent* syncEvent = m_syncEvent[0];
 		syncEvent->SetCycles(GetRegT1C() + kExtraTimerCycles);	// NB. use COUNTER, not LATCH
+		syncEvent->m_canAssertIRQ = (m_regs.IER & IxR_TIMER1) ? true : false;
 		g_SynchronousEventMgr.Insert(syncEvent);
 	}
 	if (IsTimer2Active())
 	{
 		SyncEvent* syncEvent = m_syncEvent[1];
 		syncEvent->SetCycles(GetRegT2C() + kExtraTimerCycles);	// NB. use COUNTER, not LATCH
+		syncEvent->m_canAssertIRQ = (m_regs.IER & IxR_TIMER2) ? true : false;
 		g_SynchronousEventMgr.Insert(syncEvent);
 	}
 }
diff --git a/source/CPU.cpp b/source/CPU.cpp
index 9b04deca..88621aa5 100644
--- a/source/CPU.cpp
+++ b/source/CPU.cpp
@@ -139,6 +139,9 @@ static volatile BOOL g_bNmiFlank = FALSE; // Positive going flank on NMI line
 static bool g_irqDefer1Opcode = false;
 static bool g_interruptInLastExecutionBatch = false;	// Last batch of executed cycles included an interrupt (IRQ/NMI)
 
+// NB. No need to save to save-state, as IRQ() follows CheckSynchronousInterruptSources(), and IRQ() always sets it to false.
+static bool g_irqOnLastOpcodeCycle = false;
+
 //
 
 static eCpuType g_MainCPU = CPU_65C02;
@@ -204,6 +207,12 @@ bool IsInterruptInLastExecution(void)
 	return g_interruptInLastExecutionBatch;
 }
 
+void SetIrqOnLastOpcodeCycle(void)
+{
+	if (!(regs.ps & AF_INTERRUPT))
+		g_irqOnLastOpcodeCycle = true;
+}
+
 //
 
 #include "CPU/cpu_general.inl"
@@ -406,9 +415,6 @@ static __forceinline void CheckSynchronousInterruptSources(UINT cycles, ULONG uE
 	g_SynchronousEventMgr.Update(cycles, uExecutedCycles);
 }
 
-// NB. No need to save to save-state, as IRQ() follows CheckSynchronousInterruptSources(), and IRQ() always sets it to false.
-bool g_irqOnLastOpcodeCycle = false;
-
 static __forceinline bool IRQ(ULONG& uExecutedCycles, BOOL& flagc, BOOL& flagn, BOOL& flagv, BOOL& flagz)
 {
 	bool irqTaken = false;
diff --git a/source/CPU.h b/source/CPU.h
index 90ee5204..f0bac764 100644
--- a/source/CPU.h
+++ b/source/CPU.h
@@ -61,3 +61,4 @@ bool IsIrqAsserted(void);
 bool Is6502InterruptEnabled(void);
 void ResetCyclesExecutedForDebugger(void);
 bool IsInterruptInLastExecution(void);
+void SetIrqOnLastOpcodeCycle(void);
diff --git a/source/SynchronousEventManager.cpp b/source/SynchronousEventManager.cpp
index 3ad1dfeb..c45b48b8 100644
--- a/source/SynchronousEventManager.cpp
+++ b/source/SynchronousEventManager.cpp
@@ -42,6 +42,7 @@ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 #include "StdAfx.h"
 
 #include "SynchronousEventManager.h"
+#include "CPU.h"
 
 void SynchronousEventManager::Insert(SyncEvent* pNewEvent)
 {
@@ -135,8 +136,6 @@ bool SynchronousEventManager::Remove(int id)
 	return false;
 }
 
-extern bool g_irqOnLastOpcodeCycle;
-
 void SynchronousEventManager::Update(int cycles, ULONG uExecutedCycles)
 {
 	SyncEvent* pCurrEvent = m_syncEventHead;
@@ -147,8 +146,8 @@ void SynchronousEventManager::Update(int cycles, ULONG uExecutedCycles)
 	pCurrEvent->m_cyclesRemaining -= cycles;
 	if (pCurrEvent->m_cyclesRemaining <= 0)
 	{
-		if (pCurrEvent->m_cyclesRemaining == 0)
-			g_irqOnLastOpcodeCycle = true;		// IRQ occurs on last cycle of opcode
+		if (pCurrEvent->m_cyclesRemaining == 0 && pCurrEvent->m_canAssertIRQ)
+			SetIrqOnLastOpcodeCycle();		// IRQ occurs on last cycle of opcode
 
 		int cyclesUnderflowed = -pCurrEvent->m_cyclesRemaining;
 
diff --git a/source/SynchronousEventManager.h b/source/SynchronousEventManager.h
index d0b9f621..9a48d405 100644
--- a/source/SynchronousEventManager.h
+++ b/source/SynchronousEventManager.h
@@ -32,6 +32,7 @@ public:
 		: m_id(id),
 		m_cyclesRemaining(initCycles),
 		m_active(false),
+		m_canAssertIRQ(true),
 		m_callback(callback),
 		m_next(NULL)
 	{}
@@ -45,6 +46,7 @@ public:
 	int m_id;
 	int m_cyclesRemaining;
 	bool m_active;
+	bool m_canAssertIRQ;
 	syncEventCB m_callback;
 	SyncEvent* m_next;
 };
diff --git a/test/TestCPU6502/TestCPU6502.cpp b/test/TestCPU6502/TestCPU6502.cpp
index 4354d900..8afe92c7 100644
--- a/test/TestCPU6502/TestCPU6502.cpp
+++ b/test/TestCPU6502/TestCPU6502.cpp
@@ -34,6 +34,10 @@ eCpuType GetActiveCpu(void)
 	return g_ActiveCPU;
 }
 
+void SetIrqOnLastOpcodeCycle(void)
+{
+}
+
 bool g_bStopOnBRK = false;
 
 static __forceinline int Fetch(BYTE& iOpcode, ULONG uExecutedCycles)