diff --git a/rtos/rtx/TARGET_CORTEX_A/RTX_Conf_CA.c b/rtos/rtx/TARGET_CORTEX_A/RTX_Conf_CA.c
index 96edb8e2cc0..83b5820e090 100644
--- a/rtos/rtx/TARGET_CORTEX_A/RTX_Conf_CA.c
+++ b/rtos/rtx/TARGET_CORTEX_A/RTX_Conf_CA.c
@@ -72,9 +72,9 @@
 
 //   <o>Main Thread stack size [bytes] <64-4096:8><#/4>
 //   <i> Defines stack size for main thread.
-//   <i> Default: 200
+//   <i> Default: 4096
 #ifndef OS_MAINSTKSIZE
- #define OS_MAINSTKSIZE 2048
+ #define OS_MAINSTKSIZE 4096
 #endif
 
 #ifndef __MBED_CMSIS_RTOS_CA9