diff --git a/docs/reports/LPC1114-48-GCC.txt b/docs/reports/LPC1114-48-GCC.txt
index 32ea4154e..87dd7dbbe 100644
--- a/docs/reports/LPC1114-48-GCC.txt
+++ b/docs/reports/LPC1114-48-GCC.txt
@@ -126,7 +126,7 @@ Settings: CLK=48, (2 wait states)
 --- Result: SUCCESS
 ----------------------------------------------------------------------------
 --- Test Case 11.8 (Benchmark, round robin context switching)
---- Score : 253332 ctxswc/S
+--- Score : 253328 ctxswc/S
 --- Result: SUCCESS
 ----------------------------------------------------------------------------
 --- Test Case 11.9 (Benchmark, I/O Queues throughput)
diff --git a/os/ports/GCC/ARMCMx/chcore_v6m.h b/os/ports/GCC/ARMCMx/chcore_v6m.h
index 4b4ef04f6..bb20cb4be 100644
--- a/os/ports/GCC/ARMCMx/chcore_v6m.h
+++ b/os/ports/GCC/ARMCMx/chcore_v6m.h
@@ -128,16 +128,18 @@ struct intctx {
  *          enabled to invoke system APIs.
  */
 #define PORT_IRQ_EPILOGUE() {                                               \
-  port_lock_from_isr();                                                     \
-  if ((_saved_lr != (regarm_t)0xFFFFFFF1) && chSchIsRescRequiredExI()) {    \
-    register struct cmxctx *ctxp;                                           \
+  if (_saved_lr != (regarm_t)0xFFFFFFF1) {                                  \
+    port_lock_from_isr();                                                   \
+    if (chSchIsRescRequiredExI()) {                                         \
+      register struct cmxctx *ctxp;                                         \
                                                                             \
-    asm volatile ("mrs     %0, PSP" : "=r" (ctxp) : );                      \
-    _port_saved_pc = ctxp->pc;                                              \
-    ctxp->pc = _port_switch_from_isr;                                       \
-    return;                                                                 \
+      asm volatile ("mrs     %0, PSP" : "=r" (ctxp) : );                    \
+      _port_saved_pc = ctxp->pc;                                            \
+      ctxp->pc = _port_switch_from_isr;                                     \
+      return;                                                               \
+    }                                                                       \
+    port_unlock_from_isr();                                                 \
   }                                                                         \
-  port_unlock_from_isr();                                                   \
 }
 
 /**
diff --git a/os/ports/IAR/ARMCMx/chcore_v6m.c b/os/ports/IAR/ARMCMx/chcore_v6m.c
index 25b360809..d8ede674d 100644
--- a/os/ports/IAR/ARMCMx/chcore_v6m.c
+++ b/os/ports/IAR/ARMCMx/chcore_v6m.c
@@ -32,11 +32,6 @@
  */
 regarm_t _port_saved_pc;
 
-/**
- * @brief   IRQ nesting counter.
- */
-unsigned _port_irq_nesting;
-
 /**
  * @brief   System Timer vector.
  * @details This interrupt is used as system tick.
diff --git a/os/ports/IAR/ARMCMx/chcore_v6m.h b/os/ports/IAR/ARMCMx/chcore_v6m.h
index a2d1a40d3..fdbde0641 100644
--- a/os/ports/IAR/ARMCMx/chcore_v6m.h
+++ b/os/ports/IAR/ARMCMx/chcore_v6m.h
@@ -118,18 +118,14 @@ struct intctx {
  * @details This macro must be inserted at the start of all IRQ handlers
  *          enabled to invoke system APIs.
  */
-#define PORT_IRQ_PROLOGUE() {                                               \
-  port_lock_from_isr();                                                     \
-  _port_irq_nesting++;                                                      \
-  port_unlock_from_isr();                                                   \
-}
+#define PORT_IRQ_PROLOGUE() regarm_t _saved_lr = (regarm_t)__get_LR()
 
 /**
  * @brief   IRQ epilogue code.
  * @details This macro must be inserted at the end of all IRQ handlers
  *          enabled to invoke system APIs.
  */
-#define PORT_IRQ_EPILOGUE() _port_irq_epilogue()
+#define PORT_IRQ_EPILOGUE() _port_irq_epilogue(_saved_lr)
 
 /**
  * @brief   IRQ handler function declaration.
@@ -149,7 +145,6 @@ struct intctx {
  * @brief   Port-related initialization code.
  */
 #define port_init() {                                                       \
-  _port_irq_nesting = 0;                                                    \
   SCB_AIRCR = AIRCR_VECTKEY | AIRCR_PRIGROUP(0);                            \
   NVICSetSystemHandlerPriority(HANDLER_SYSTICK,                             \
     CORTEX_PRIORITY_MASK(CORTEX_PRIORITY_SYSTICK));                         \
@@ -238,7 +233,6 @@ struct intctx {
 
 #if !defined(__DOXYGEN__)
 extern regarm_t _port_saved_pc;
-extern unsigned _port_irq_nesting;
 #endif
 
 #ifdef __cplusplus
@@ -246,7 +240,7 @@ extern "C" {
 #endif
   void port_halt(void);
   void _port_switch(Thread *ntp, Thread *otp);
-  void _port_irq_epilogue(void);
+  void _port_irq_epilogue(regarm_t lr);
   void _port_switch_from_isr(void);
   void _port_thread_start(void);
 #ifdef __cplusplus
diff --git a/os/ports/IAR/ARMCMx/chcoreasm_v6m.s b/os/ports/IAR/ARMCMx/chcoreasm_v6m.s
index 1b8a5583c..5333d4ab9 100644
--- a/os/ports/IAR/ARMCMx/chcoreasm_v6m.s
+++ b/os/ports/IAR/ARMCMx/chcoreasm_v6m.s
@@ -105,27 +105,23 @@ _port_switch_from_isr:
  */
         PUBLIC  _port_irq_epilogue
 _port_irq_epilogue:
-        push    {r4, lr}
+        push    {r3, lr}
+        adds    r0, r0, #15
+        beq     stillnested
         cpsid   i
-        ldr     r2, =_port_irq_nesting
-        ldr     r3, [r2]
-        subs    r3, r3, #1
-        str     r3, [r2]
-        cmp     r3, #0
-        beq     skipexit
-notrequired
-        cpsie   i
-        pop     {r4, pc}
-skipexit
         bl      chSchIsRescRequiredExI
         cmp     r0, #0
-        beq     notrequired
-        mrs     r1, PSP
+        bne     doresch
+        cpsie   i
+stillnested
+        pop     {r3, pc}
+doresch
+        mrs     r3, PSP
         ldr     r2, =_port_saved_pc
-        ldr     r3, [r1, #24]
-        str     r3, [r2]
-        ldr     r3, =_port_switch_from_isr
-        str     r3, [r1, #24]
-        pop     {r4, pc}
+        ldr     r1, [r3, #24]
+        str     r1, [r2]
+        ldr     r2, =_port_switch_from_isr
+        str     r2, [r3, #24]
+        pop     {r3, pc}
 
         END
diff --git a/readme.txt b/readme.txt
index 6c5174cfa..6a78aa5d2 100644
--- a/readme.txt
+++ b/readme.txt
@@ -69,7 +69,8 @@
 *****************************************************************************
 
 *** 2.3.0 ***
-- FIX: Fixed race condition in CM0 ports (bug 3193062)(backported to 2.2.2).
+- FIX: Fixed race condition in CM0 ports, the fix also improves the
+  ISR latency (bug 3193062)(backported to 2.2.2).
 - FIX: Fixed Cortex-Mx linker scripts alignment of __heap_base__, the
   correct alignment is now enforced at runtime into core_init() in order
   to make the OS integration easier (bug 3191112)(backported to 2.2.2).