diff --git a/libraries/mbed/targets/cmsis/TARGET_NORDIC/TARGET_NRF51822/system_nrf51822.c b/libraries/mbed/targets/cmsis/TARGET_NORDIC/TARGET_NRF51822/system_nrf51822.c
index 8601747662..c9d19aeca6 100644
--- a/libraries/mbed/targets/cmsis/TARGET_NORDIC/TARGET_NRF51822/system_nrf51822.c
+++ b/libraries/mbed/targets/cmsis/TARGET_NORDIC/TARGET_NRF51822/system_nrf51822.c
@@ -11,17 +11,13 @@
  */
 
 
-
-/* NOTE: Template files (including this one) are application specific and therefore expected to 
-   be copied into the application project folder prior to its use! */
-
 #include <stdint.h>
 #include <stdbool.h>
 #include "nrf51822.h"
 #include "system_nrf51822.h"
 
 
-#define __SYSTEM_CLOCK      (16000000UL)     /*!< nRF51 devices use a fixed System Clock Frequency of 16MHz */
+#define __SYSTEM_CLOCK      (16000000UL)     //!< nRF51 devices use a fixed System Clock Frequency of 16MHz
 
 static bool is_manual_peripheral_setup_needed(void);
 static bool is_disabled_in_debug_needed(void);
@@ -43,7 +39,8 @@ void SystemCoreClockUpdate(void)
 
 void SystemInit(void)
 {
-    /* Write the necessary UICR values if needed */
+
+    //Write the necessary UICR and FWID values if needed
     if (NRF_UICR->CLENR0 == 0xFFFFFFFF){
         NRF_NVMC->CONFIG = (NVMC_CONFIG_WEN_Wen << NVMC_CONFIG_WEN_Pos);
         while (NRF_NVMC->READY == NVMC_READY_READY_Busy){
@@ -53,7 +50,9 @@ void SystemInit(void)
         while (NRF_NVMC->READY == NVMC_READY_READY_Busy){
         }
         
-        NRF_UICR->FWID = 0xFFFF0049;
+        //write FWID (NRF_UICR->FWID is readonly)
+        *(uint32_t *)0x10001010 = 0xFFFF0049;
+       
         while (NRF_NVMC->READY == NVMC_READY_READY_Busy){
         }
         
@@ -66,19 +65,20 @@ void SystemInit(void)
         }
     }
     
-    /* Prepare the peripherals for use as indicated by the PAN 26 "System: Manual setup is required
-       to enable the use of peripherals" found at Product Anomaly document for your device found at
-       https://www.nordicsemi.com/. The side effect of executing these instructions in the devices 
-       that do not need it is that the new peripherals in the second generation devices (LPCOMP for
-       example) will not be available. */
+    // Prepare the peripherals for use as indicated by the PAN 26 "System: Manual setup is required
+    // to enable the use of peripherals" found at Product Anomaly document for your device found at
+    // https://www.nordicsemi.com/. The side effect of executing these instructions in the devices 
+    // that do not need it is that the new peripherals in the second generation devices (LPCOMP for
+    // example) will not be available.
+    
     if (is_manual_peripheral_setup_needed()){
         *(uint32_t volatile *)0x40000504 = 0xC007FFDF;
         *(uint32_t volatile *)0x40006C18 = 0x00008000;
     }
     
-    /* Disable PROTENSET registers under debug, as indicated by PAN 59 "MPU: Reset value of DISABLEINDEBUG
-       register is incorrect" found at Product Anomaly document four your device found at 
-       https://www.nordicsemi.com/. There is no side effect of using these instruction if not needed. */
+    // Disable PROTENSET registers under debug, as indicated by PAN 59 "MPU: Reset value of DISABLEINDEBUG
+    // register is incorrect" found at Product Anomaly document four your device found at 
+    // https://www.nordicsemi.com/. There is no side effect of using these instruction if not needed. 
     if (is_disabled_in_debug_needed()){
         NRF_MPU->DISABLEINDEBUG = MPU_DISABLEINDEBUG_DISABLEINDEBUG_Disabled << MPU_DISABLEINDEBUG_DISABLEINDEBUG_Pos;
     }