diff --git a/tools/toolchains/__init__.py b/tools/toolchains/__init__.py
index 053784876a..489d09caab 100644
--- a/tools/toolchains/__init__.py
+++ b/tools/toolchains/__init__.py
@@ -166,14 +166,14 @@ class mbedToolchain:
     VERBOSE = True
 
     CORTEX_SYMBOLS = {
-        "Cortex-M0" : ["__CORTEX_M0", "ARM_MATH_CM0"],
-        "Cortex-M0+": ["__CORTEX_M0PLUS", "ARM_MATH_CM0PLUS"],
+        "Cortex-M0" : ["__CORTEX_M0", "ARM_MATH_CM0", "__CMSIS_RTOS", "__MBED_CMSIS_RTOS_CM"],
+        "Cortex-M0+": ["__CORTEX_M0PLUS", "ARM_MATH_CM0PLUS", "__CMSIS_RTOS", "__MBED_CMSIS_RTOS_CM"],
         "Cortex-M1" : ["__CORTEX_M3", "ARM_MATH_CM1"],
-        "Cortex-M3" : ["__CORTEX_M3", "ARM_MATH_CM3"],
-        "Cortex-M4" : ["__CORTEX_M4", "ARM_MATH_CM4"],
-        "Cortex-M4F" : ["__CORTEX_M4", "ARM_MATH_CM4", "__FPU_PRESENT=1"],
-        "Cortex-M7" : ["__CORTEX_M7", "ARM_MATH_CM7"],
-        "Cortex-M7F" : ["__CORTEX_M7", "ARM_MATH_CM7", "__FPU_PRESENT=1"],
+        "Cortex-M3" : ["__CORTEX_M3", "ARM_MATH_CM3", "__CMSIS_RTOS", "__MBED_CMSIS_RTOS_CM"],
+        "Cortex-M4" : ["__CORTEX_M4", "ARM_MATH_CM4", "__CMSIS_RTOS", "__MBED_CMSIS_RTOS_CM"],
+        "Cortex-M4F" : ["__CORTEX_M4", "ARM_MATH_CM4", "__FPU_PRESENT=1", "__CMSIS_RTOS", "__MBED_CMSIS_RTOS_CM"],
+        "Cortex-M7" : ["__CORTEX_M7", "ARM_MATH_CM7", "__CMSIS_RTOS", "__MBED_CMSIS_RTOS_CM"],
+        "Cortex-M7F" : ["__CORTEX_M7", "ARM_MATH_CM7", "__FPU_PRESENT=1", "__CMSIS_RTOS", "__MBED_CMSIS_RTOS_CM"],
         "Cortex-A9" : ["__CORTEX_A9", "ARM_MATH_CA9", "__FPU_PRESENT", "__CMSIS_RTOS", "__EVAL", "__MBED_CMSIS_RTOS_CA9"],
     }