diff --git a/cmsis/CMSIS_5/CMSIS/RTOS2/RTX/CMakeLists.txt b/cmsis/CMSIS_5/CMSIS/RTOS2/RTX/CMakeLists.txt
index 24d9f345c3..2a3d39f279 100644
--- a/cmsis/CMSIS_5/CMSIS/RTOS2/RTX/CMakeLists.txt
+++ b/cmsis/CMSIS_5/CMSIS/RTOS2/RTX/CMakeLists.txt
@@ -15,6 +15,8 @@ function(_mbed_get_cortex_m_exception_handlers toolchain_dir)
             set(STARTUP_RTX_FILE TARGET_M3/irq_cm3.S)
         elseif(${key} STREQUAL M33)
             set(STARTUP_RTX_FILE TARGET_M33/irq_armv8mml.S)
+        elseif(${key} STREQUAL M55)
+            set(STARTUP_RTX_FILE TARGET_M33/irq_armv8mml.S)
         elseif(${key} STREQUAL RTOS_M4_M7)
             set(STARTUP_RTX_FILE TARGET_RTOS_M4_M7/irq_cm4f.S)
         endif()