diff --git a/list.c b/list.c
index 5d1dc9e79..9069a2252 100644
--- a/list.c
+++ b/list.c
@@ -158,6 +158,7 @@ void vListInsert( List_t * const pxList,
         *   4) Using a queue or semaphore before it has been initialised or
         *      before the scheduler has been started (are interrupts firing
         *      before vTaskStartScheduler() has been called?).
+        *   5) Misconfigured SysTick priority? Must be lowest (logical) priority.
         **********************************************************************/
 
         for( pxIterator = ( ListItem_t * ) &( pxList->xListEnd ); pxIterator->pxNext->xItemValue <= xValueOfInsertion; pxIterator = pxIterator->pxNext ) /*lint !e826 !e740 !e9087 The mini list structure is used as the list end to save RAM.  This is checked and valid. *//*lint !e440 The iterator moves to a different value, not xValueOfInsertion. */
diff --git a/portable/CCS/ARM_CM3/port.c b/portable/CCS/ARM_CM3/port.c
index afd2ff07d..c61297bcc 100644
--- a/portable/CCS/ARM_CM3/port.c
+++ b/portable/CCS/ARM_CM3/port.c
@@ -331,6 +331,9 @@ void vPortExitCritical( void )
 
 void xPortSysTickHandler( void )
 {
+    /* The SysTick is not allowed to interrupt a critical section. */
+    configAssert( uxCriticalNesting == 0 )
+
     /* The SysTick runs at the lowest interrupt priority, so when this interrupt
      * executes all interrupts must be unmasked.  There is therefore no need to
      * save and then restore the interrupt mask value as its value is already
diff --git a/portable/CCS/ARM_CM4F/port.c b/portable/CCS/ARM_CM4F/port.c
index 19ff798c8..fd537f256 100644
--- a/portable/CCS/ARM_CM4F/port.c
+++ b/portable/CCS/ARM_CM4F/port.c
@@ -356,6 +356,9 @@ void vPortExitCritical( void )
 
 void xPortSysTickHandler( void )
 {
+    /* The SysTick is not allowed to interrupt a critical section. */
+    configAssert( uxCriticalNesting == 0 )
+
     /* The SysTick runs at the lowest interrupt priority, so when this interrupt
      * executes all interrupts must be unmasked.  There is therefore no need to
      * save and then restore the interrupt mask value as its value is already
diff --git a/portable/GCC/ARM_CM3/port.c b/portable/GCC/ARM_CM3/port.c
index 2546ffaf9..b2684e994 100644
--- a/portable/GCC/ARM_CM3/port.c
+++ b/portable/GCC/ARM_CM3/port.c
@@ -431,6 +431,9 @@ void xPortPendSVHandler( void )
 
 void xPortSysTickHandler( void )
 {
+    /* The SysTick is not allowed to interrupt a critical section. */
+    configAssert( uxCriticalNesting == 0 )
+
     /* The SysTick runs at the lowest interrupt priority, so when this interrupt
      * executes all interrupts must be unmasked.  There is therefore no need to
      * save and then restore the interrupt mask value as its value is already
diff --git a/portable/GCC/ARM_CM4F/port.c b/portable/GCC/ARM_CM4F/port.c
index f05a48f42..2d90c2d67 100644
--- a/portable/GCC/ARM_CM4F/port.c
+++ b/portable/GCC/ARM_CM4F/port.c
@@ -493,6 +493,9 @@ void xPortPendSVHandler( void )
 
 void xPortSysTickHandler( void )
 {
+    /* The SysTick is not allowed to interrupt a critical section. */
+    configAssert( uxCriticalNesting == 0 )
+
     /* The SysTick runs at the lowest interrupt priority, so when this interrupt
      * executes all interrupts must be unmasked.  There is therefore no need to
      * save and then restore the interrupt mask value as its value is already
diff --git a/portable/GCC/ARM_CM7/r0p1/port.c b/portable/GCC/ARM_CM7/r0p1/port.c
index f9e240e58..e79ac1809 100644
--- a/portable/GCC/ARM_CM7/r0p1/port.c
+++ b/portable/GCC/ARM_CM7/r0p1/port.c
@@ -483,6 +483,9 @@ void xPortPendSVHandler( void )
 
 void xPortSysTickHandler( void )
 {
+    /* The SysTick is not allowed to interrupt a critical section. */
+    configAssert( uxCriticalNesting == 0 )
+
     /* The SysTick runs at the lowest interrupt priority, so when this interrupt
      * executes all interrupts must be unmasked.  There is therefore no need to
      * save and then restore the interrupt mask value as its value is already
diff --git a/portable/IAR/ARM_CM3/port.c b/portable/IAR/ARM_CM3/port.c
index e2d3662de..30082e176 100644
--- a/portable/IAR/ARM_CM3/port.c
+++ b/portable/IAR/ARM_CM3/port.c
@@ -334,6 +334,9 @@ void vPortExitCritical( void )
 
 void xPortSysTickHandler( void )
 {
+    /* The SysTick is not allowed to interrupt a critical section. */
+    configAssert( uxCriticalNesting == 0 )
+
     /* The SysTick runs at the lowest interrupt priority, so when this interrupt
      * executes all interrupts must be unmasked.  There is therefore no need to
      * save and then restore the interrupt mask value as its value is already
diff --git a/portable/IAR/ARM_CM4F/port.c b/portable/IAR/ARM_CM4F/port.c
index e180aede0..a024086b6 100644
--- a/portable/IAR/ARM_CM4F/port.c
+++ b/portable/IAR/ARM_CM4F/port.c
@@ -371,6 +371,9 @@ void vPortExitCritical( void )
 
 void xPortSysTickHandler( void )
 {
+    /* The SysTick is not allowed to interrupt a critical section. */
+    configAssert( uxCriticalNesting == 0 )
+
     /* The SysTick runs at the lowest interrupt priority, so when this interrupt
      * executes all interrupts must be unmasked.  There is therefore no need to
      * save and then restore the interrupt mask value as its value is already
diff --git a/portable/IAR/ARM_CM4F_MPU/port.c b/portable/IAR/ARM_CM4F_MPU/port.c
index 6fd318fc3..58905ceda 100644
--- a/portable/IAR/ARM_CM4F_MPU/port.c
+++ b/portable/IAR/ARM_CM4F_MPU/port.c
@@ -483,6 +483,9 @@ void vPortExitCritical( void )
 
 void xPortSysTickHandler( void )
 {
+    /* The SysTick is not allowed to interrupt a critical section. */
+    configAssert( uxCriticalNesting == 0 )
+
     /* The SysTick runs at the lowest interrupt priority, so when this interrupt
      * executes all interrupts must be unmasked.  There is therefore no need to
      * save and then restore the interrupt mask value as its value is already
diff --git a/portable/IAR/ARM_CM7/r0p1/port.c b/portable/IAR/ARM_CM7/r0p1/port.c
index 71caa71e1..48375134a 100644
--- a/portable/IAR/ARM_CM7/r0p1/port.c
+++ b/portable/IAR/ARM_CM7/r0p1/port.c
@@ -359,6 +359,9 @@ void vPortExitCritical( void )
 
 void xPortSysTickHandler( void )
 {
+    /* The SysTick is not allowed to interrupt a critical section. */
+    configAssert( uxCriticalNesting == 0 )
+
     /* The SysTick runs at the lowest interrupt priority, so when this interrupt
      * executes all interrupts must be unmasked.  There is therefore no need to
      * save and then restore the interrupt mask value as its value is already
diff --git a/portable/MikroC/ARM_CM4F/port.c b/portable/MikroC/ARM_CM4F/port.c
index 33fc346a6..cfd350f3b 100644
--- a/portable/MikroC/ARM_CM4F/port.c
+++ b/portable/MikroC/ARM_CM4F/port.c
@@ -485,6 +485,9 @@ void xPortPendSVHandler( void ) iv IVT_INT_PendSV ics ICS_OFF
 
 void xPortSysTickHandler( void ) iv IVT_INT_SysTick ics ICS_AUTO
 {
+    /* The SysTick is not allowed to interrupt a critical section. */
+    configAssert( uxCriticalNesting == 0 )
+
     /* The SysTick runs at the lowest interrupt priority, so when this interrupt
      * executes all interrupts must be unmasked.  There is therefore no need to
      * save and then restore the interrupt mask value as its value is already
diff --git a/portable/RVDS/ARM_CM3/port.c b/portable/RVDS/ARM_CM3/port.c
index 6de6a2568..22a504ae2 100644
--- a/portable/RVDS/ARM_CM3/port.c
+++ b/portable/RVDS/ARM_CM3/port.c
@@ -424,6 +424,9 @@ __asm void xPortPendSVHandler( void )
 
 void xPortSysTickHandler( void )
 {
+    /* The SysTick is not allowed to interrupt a critical section. */
+    configAssert( uxCriticalNesting == 0 )
+
     /* The SysTick runs at the lowest interrupt priority, so when this interrupt
      * executes all interrupts must be unmasked.  There is therefore no need to
      * save and then restore the interrupt mask value as its value is already
diff --git a/portable/RVDS/ARM_CM4F/port.c b/portable/RVDS/ARM_CM4F/port.c
index 5f4ac1754..1eba09b17 100644
--- a/portable/RVDS/ARM_CM4F/port.c
+++ b/portable/RVDS/ARM_CM4F/port.c
@@ -516,6 +516,9 @@ __asm void xPortPendSVHandler( void )
 
 void xPortSysTickHandler( void )
 {
+    /* The SysTick is not allowed to interrupt a critical section. */
+    configAssert( uxCriticalNesting == 0 )
+
     /* The SysTick runs at the lowest interrupt priority, so when this interrupt
      * executes all interrupts must be unmasked.  There is therefore no need to
      * save and then restore the interrupt mask value as its value is already
diff --git a/portable/RVDS/ARM_CM7/r0p1/port.c b/portable/RVDS/ARM_CM7/r0p1/port.c
index 17e16f3e3..a7305c659 100644
--- a/portable/RVDS/ARM_CM7/r0p1/port.c
+++ b/portable/RVDS/ARM_CM7/r0p1/port.c
@@ -503,6 +503,9 @@ __asm void xPortPendSVHandler( void )
 
 void xPortSysTickHandler( void )
 {
+    /* The SysTick is not allowed to interrupt a critical section. */
+    configAssert( uxCriticalNesting == 0 )
+
     /* The SysTick runs at the lowest interrupt priority, so when this interrupt
      * executes all interrupts must be unmasked.  There is therefore no need to
      * save and then restore the interrupt mask value as its value is already