diff --git a/os/rt/include/chsys.h b/os/rt/include/chsys.h
index fc789012a..01742c946 100644
--- a/os/rt/include/chsys.h
+++ b/os/rt/include/chsys.h
@@ -332,6 +332,7 @@ extern "C" {
 #endif
   void chSysWaitSystemState(system_state_t state);
   void chSysInit(void);
+  thread_t *chSysGetIdleThreadX(void);
   bool chSysIntegrityCheckI(unsigned testmask);
   void chSysTimerHandlerI(void);
   syssts_t chSysGetStatusAndLockX(void);
@@ -518,25 +519,6 @@ static inline void chSysNotifyInstance(os_instance_t *oip) {
 }
 #endif
 
-#if (CH_CFG_NO_IDLE_THREAD == FALSE) || defined(__DOXYGEN__)
-/**
- * @brief   Returns a pointer to the idle thread.
- * @pre     In order to use this function the option @p CH_CFG_NO_IDLE_THREAD
- *          must be disabled.
- * @note    The reference counter of the idle thread is not incremented but
- *          it is not strictly required being the idle thread a static
- *          object.
- *
- * @return              Pointer to the idle thread.
- *
- * @xclass
- */
-static inline thread_t *chSysGetIdleThreadX(void) {
-
-  return threadref(currcore->rlist.pqueue.prev);
-}
-#endif /* CH_CFG_NO_IDLE_THREAD == FALSE */
-
 #endif /* CHSYS_H */
 
 /** @} */
diff --git a/os/rt/src/chsys.c b/os/rt/src/chsys.c
index d0f3bb68d..7b3ec3f5b 100644
--- a/os/rt/src/chsys.c
+++ b/os/rt/src/chsys.c
@@ -55,6 +55,7 @@ CH_SYS_CORE0_MEMORY os_instance_t ch0;
  */
 static CH_SYS_CORE0_MEMORY THD_WORKING_AREA(ch_c0_idle_thread_wa,
                                             PORT_IDLE_THREAD_STACK_SIZE);
+#endif
 
 #if CH_DBG_ENABLE_STACK_CHECK == TRUE
 extern stkalign_t __main_thread_stack_base__, __main_thread_stack_end__;
@@ -77,7 +78,6 @@ const os_instance_config_t ch_core0_cfg = {
   .idlethread_end   = THD_WORKING_AREA_END(ch_c0_idle_thread_wa)
 #endif
 };
-#endif
 
 #if (PORT_CORES_NUMBER > 1) || defined(__DOXYGEN__)
 /**
@@ -233,6 +233,26 @@ void chSysHalt(const char *reason) {
   }
 }
 
+/**
+ * @brief   Returns a pointer to the idle thread.
+ * @note    The reference counter of the idle thread is not incremented but
+ *          it is not strictly required being the idle thread a static
+ *          object.
+ * @note    This function cannot be called from the idle thread itself,
+ *          use @p chThdGetSelfX() in that case.
+ *
+ * @return              Pointer to the idle thread.
+ *
+ * @xclass
+ */
+thread_t *chSysGetIdleThreadX(void) {
+  thread_t *tp = threadref(currcore->rlist.pqueue.prev);
+
+  chDbgAssert(tp->hdr.pqueue.prio == IDLEPRIO, "not idle thread");
+
+  return tp;
+}
+
 /**
  * @brief   System integrity check.
  * @details Performs an integrity check of the important ChibiOS/RT data
diff --git a/readme.txt b/readme.txt
index 7bb0d0475..84cf0a16b 100644
--- a/readme.txt
+++ b/readme.txt
@@ -78,34 +78,38 @@
 - NEW: EFL driver and demo for STM32F3xx.
 - NEW: New unit test subsystem under /os/test. Now it is officially
        ChibiOS/TEST.
-- FIX: Fixed STM32 ADCv3 differences in headers (bug #1182)
-       (backported to 20.3.4).
-- FIX: Fixed DMAv1 compile fail on STM32L011 (bug #1181)
-       (backported to 20.3.4).
-- FIX: Fixed error in STM32_ADCCLK_MIN for STM32F37x/hal_lld.h (bug #1180)
-       (backported to 20.3.4).
-- FIX: Fixed direct calls to RT in STM32 RTCv2 and RTCv3 (bug #1179)
-       (backported to 20.3.4).
-- FIX: Fixed STM32G071 mcuconf.h template not showing TIM14/15/16/17
-       (bug #1178).
-- FIX: Fixed path ambiguity between STM32 USARTv2 and USARTv3 drivers
-       (bug #1177).
-- FIX: Fixed invalid DMAMUX settings in DMAv1 for some devices (bug #1176)
-       (backported to 20.3.4).
-- FIX: Fixed wrong macro in the demo STM32F7xx-SPI-ADXL355 (bug #1175) 
+- FIX: Fixed CH_CFG_NO_IDLE_THREAD option causes compiler errors (bug #1183) 
        (backported to 21.6.1).
+- FIX: Fixed STM32 ADCv3 differences in headers (bug #1182)
+       (backported to 21.6.1)(backported to 20.3.4).
+- FIX: Fixed DMAv1 compile fail on STM32L011 (bug #1181)
+       (backported to 21.6.1)(backported to 20.3.4).
+- FIX: Fixed error in STM32_ADCCLK_MIN for STM32F37x/hal_lld.h (bug #1180)
+       (backported to 21.6.1)(backported to 20.3.4).
+- FIX: Fixed direct calls to RT in STM32 RTCv2 and RTCv3 (bug #1179)
+       (backported to 21.6.1)(backported to 20.3.4).
+- FIX: Fixed STM32G071 mcuconf.h template not showing TIM14/15/16/17
+       (bug #1178)(backported to 21.6.1).
+- FIX: Fixed path ambiguity between STM32 USARTv2 and USARTv3 drivers
+       (bug #1177)(backported to 21.6.1).
+- FIX: Fixed invalid DMAMUX settings in DMAv1 for some devices (bug #1176)
+       (backported to 21.6.1)(backported to 20.3.4).
+- FIX: Fixed wrong macro in the demo STM32F7xx-SPI-ADXL355 (bug #1175) 
+       (backported to 21.6.1(backported to 21.6.1).
 - FIX: Fixed problem with RC initialization mask of the GPIO for the 
-       STM32L4x3 (bug #1174)(backported to 20.3.4).
+       STM32L4x3 (bug #1174)(backported to 21.6.1)(backported to 20.3.4).
 - FIX: Fixed problem with N25Q driver (bug #1173)
        (backported to 21.6.1)(backported to 20.3.4).
 - FIX: Fixed semaphores broken when CH_CFG_USE_SEMAPHORES_PRIORITY is enabled
-       (bug #1172).
+       (bug #1172)(backported to 21.6.1).
 - FIX: Fixed idle thread stack area not cleared when CH_DBG_FILL_THREADS
-       is enabled (bug #1171).
+       is enabled (bug #1171)(backported to 21.6.1).
 - FIX: Fixed function chRegNextThread() broken when CH_CFG_USE_DYNAMIC
-       is disabled (bug #1170).
-- FIX: Fixed insufficient information in RT registry (bug #1169).
-- FIX: Fixed code base not compatible with -Wcast-align=strict (bug #1168).
+       is disabled (bug #1170)(backported to 21.6.1).
+- FIX: Fixed insufficient information in RT registry (bug #1169)
+       (backported to 21.6.1).
+- FIX: Fixed code base not compatible with -Wcast-align=strict (bug #1168)
+       (backported to 21.6.1).
 - FIX: Fixed wrong chconf.h for ADuCM36x demos (bug #1167)
        (backported to 21.6.1).
 - FIX: Fixed missing constant in ADuCM36x hal_lld.c (bug #1166)