diff --git a/targets/targets.json b/targets/targets.json
index 38c1f5c3ea..f9d21db375 100644
--- a/targets/targets.json
+++ b/targets/targets.json
@@ -2006,7 +2006,7 @@
         "inherits": ["Target"],
         "core": "Cortex-M0",
         "OVERRIDE_BOOTLOADER_FILENAME": "nrf51822_bootloader.hex",
-        "macros": ["NRF51", "TARGET_NRF51822", "CMSIS_VECTAB_VIRTUAL", "CMSIS_VECTAB_VIRTUAL_HEADER_FILE=\"cmsis_nvic.h\""],
+        "macros": ["NRF51", "TARGET_NRF51822", "CMSIS_VECTAB_VIRTUAL", "CMSIS_VECTAB_VIRTUAL_HEADER_FILE=\"cmsis_nvic.h\"", "MBED_CPU_UID_SIZE=8"],
         "MERGE_BOOTLOADER": false,
         "extra_labels": ["NORDIC", "MCU_NRF51", "MCU_NRF51822"],
         "OUTPUT_EXT": "hex",
@@ -3352,7 +3352,7 @@
     "MCU_NRF52840": {
         "inherits": ["Target"],
         "core": "Cortex-M4F",
-        "macros": ["TARGET_NRF52840", "BLE_STACK_SUPPORT_REQD", "SOFTDEVICE_PRESENT", "S140", "NRF_SD_BLE_API_VERSION=5", "NRF52840_XXAA", "NRF_DFU_SETTINGS_VERSION=1", "NRF_SD_BLE_API_VERSION=5", "CMSIS_VECTAB_VIRTUAL", "CMSIS_VECTAB_VIRTUAL_HEADER_FILE=\"cmsis_nvic.h\"", "MBED_TICKLESS"],
+        "macros": ["TARGET_NRF52840", "BLE_STACK_SUPPORT_REQD", "SOFTDEVICE_PRESENT", "S140", "NRF_SD_BLE_API_VERSION=5", "NRF52840_XXAA", "NRF_DFU_SETTINGS_VERSION=1", "NRF_SD_BLE_API_VERSION=5", "CMSIS_VECTAB_VIRTUAL", "CMSIS_VECTAB_VIRTUAL_HEADER_FILE=\"cmsis_nvic.h\"", "MBED_TICKLESS", "MBED_CPU_UID_SIZE=8"],
         "device_has": ["STCLK_OFF_DURING_SLEEP", "CPUUID"],
         "extra_labels": ["NORDIC", "MCU_NRF52840", "NRF5", "SDK13", "NRF52_COMMON"],
         "OUTPUT_EXT": "hex",