diff --git a/targets/TARGET_RENESAS/TARGET_RZ_A1XX/TARGET_VK_RZ_A1H/device/os_tick_ostm.c b/targets/TARGET_RENESAS/TARGET_RZ_A1XX/TARGET_VK_RZ_A1H/device/os_tick_ostm.c
index 85540192b3..e974310cea 100644
--- a/targets/TARGET_RENESAS/TARGET_RZ_A1XX/TARGET_VK_RZ_A1H/device/os_tick_ostm.c
+++ b/targets/TARGET_RENESAS/TARGET_RZ_A1XX/TARGET_VK_RZ_A1H/device/os_tick_ostm.c
@@ -191,5 +191,10 @@ uint32_t OS_Tick_GetOverflow (void)
   return (IRQ_GetPending(OSTM_IRQn));
 }
 
+// Get Cortex-A9 OS Timer interrupt number
+IRQn_ID_t mbed_get_a9_tick_irqn(){
+  return OSTM_IRQn;
+}
+
 #endif