diff --git a/rtos/mbed_lib.json b/rtos/mbed_lib.json
index c0d9e20bdc8..359a6ab8a16 100644
--- a/rtos/mbed_lib.json
+++ b/rtos/mbed_lib.json
@@ -1,6 +1,7 @@
 {
     "name": "rtos",
     "config": {
-        "present": 1
+        "present": 1,
+        "default_stack_size": "(WORDS_STACK_SIZE*4)"
     }
 }
diff --git a/rtos/rtx/TARGET_CORTEX_A/cmsis_os.h b/rtos/rtx/TARGET_CORTEX_A/cmsis_os.h
index 5ead34c9932..b1a6c770f44 100644
--- a/rtos/rtx/TARGET_CORTEX_A/cmsis_os.h
+++ b/rtos/rtx/TARGET_CORTEX_A/cmsis_os.h
@@ -149,7 +149,11 @@ used throughout the whole project.
 #    define WORDS_STACK_SIZE   128
 #endif
 
-#define DEFAULT_STACK_SIZE         (WORDS_STACK_SIZE*4)
+#ifndef MBED_CONF_RTOS_DEFAULT_STACK_SIZE
+#define MBED_CONF_RTOS_DEFAULT_STACK_SIZE (WORDS_STACK_SIZE*4)
+#endif
+
+#define DEFAULT_STACK_SIZE         MBED_CONF_RTOS_DEFAULT_STACK_SIZE
 
 /// \note MUST REMAIN UNCHANGED: \b osFeature_xxx shall be consistent in every CMSIS-RTOS.
 #define osFeature_MainThread   1       ///< main thread      1=main can be thread, 0=not available
diff --git a/rtos/rtx/TARGET_CORTEX_M/cmsis_os.h b/rtos/rtx/TARGET_CORTEX_M/cmsis_os.h
index ac052ff82b8..ed9aacb98b1 100644
--- a/rtos/rtx/TARGET_CORTEX_M/cmsis_os.h
+++ b/rtos/rtx/TARGET_CORTEX_M/cmsis_os.h
@@ -82,7 +82,11 @@
 
 #endif
 
-#define DEFAULT_STACK_SIZE         (WORDS_STACK_SIZE*4)
+#ifndef MBED_CONF_RTOS_DEFAULT_STACK_SIZE
+#define MBED_CONF_RTOS_DEFAULT_STACK_SIZE (WORDS_STACK_SIZE*4)
+#endif
+ 
+#define DEFAULT_STACK_SIZE         MBED_CONF_RTOS_DEFAULT_STACK_SIZE
 
 #define osCMSIS           0x10002U     ///< CMSIS-RTOS API version (main [31:16] .sub [15:0])