diff --git a/os/ports/GCC/ARMCMx/chcore_v6m.h b/os/ports/GCC/ARMCMx/chcore_v6m.h
index b76aa075a..0b0a41858 100644
--- a/os/ports/GCC/ARMCMx/chcore_v6m.h
+++ b/os/ports/GCC/ARMCMx/chcore_v6m.h
@@ -106,7 +106,7 @@ struct intctx {
  *          a stack frame when compiling without optimizations.
  */
 #ifndef IDLE_THREAD_STACK_SIZE
-#define IDLE_THREAD_STACK_SIZE      4
+#define IDLE_THREAD_STACK_SIZE      8
 #endif
 
 /**
@@ -120,7 +120,7 @@ struct intctx {
  *          representing the frame of the function @p chSchDoRescheduleI().
  */
 #ifndef INT_REQUIRED_STACK
-#define INT_REQUIRED_STACK          8
+#define INT_REQUIRED_STACK          16
 #endif
 
 /**
diff --git a/os/ports/GCC/ARMCMx/chcore_v7m.h b/os/ports/GCC/ARMCMx/chcore_v7m.h
index 0c8abcd41..1461a0745 100644
--- a/os/ports/GCC/ARMCMx/chcore_v7m.h
+++ b/os/ports/GCC/ARMCMx/chcore_v7m.h
@@ -96,7 +96,7 @@ struct intctx {
  *          reduce this value to zero when compiling with optimizations.
  */
 #ifndef IDLE_THREAD_STACK_SIZE
-#define IDLE_THREAD_STACK_SIZE      4
+#define IDLE_THREAD_STACK_SIZE      8
 #endif
 
 /**
@@ -106,11 +106,12 @@ struct intctx {
  *          This value can be zero on those architecture where there is a
  *          separate interrupt stack and the stack space between @p intctx and
  *          @p extctx is known to be zero.
- * @note    In this port it is set to 8 because the function
- *          @p chSchDoRescheduleI() has a stack frame.
+ * @note    In this port it is conservatively set to 16 because the function
+ *          @p chSchDoRescheduleI() can have a stack frame, expecially with
+ *          compiler optimizations disabled.
  */
 #ifndef INT_REQUIRED_STACK
-#define INT_REQUIRED_STACK          8
+#define INT_REQUIRED_STACK          16
 #endif
 
 /**
diff --git a/readme.txt b/readme.txt
index dd7a74714..ac5039db5 100644
--- a/readme.txt
+++ b/readme.txt
@@ -61,6 +61,8 @@
 *****************************************************************************
 
 *** 2.1.1 ***
+- FIX: Fixed insufficient stack size for idle thread (bug 3033624)(backported
+  to 2.0.3).
 - FIX: Fixed misspelled word in some chioch.h and chstreams.h macros (bug
   3031534)(backported to 2.0.3).
 - FIX: Fixed wrong macro check in the STM32 SPI driver (bug 3028562)(backported