diff --git a/targets/TARGET_NUVOTON/TARGET_M451/watchdog_api.c b/targets/TARGET_NUVOTON/TARGET_M451/watchdog_api.c
index af1e864c15..1ac841e78e 100644
--- a/targets/TARGET_NUVOTON/TARGET_M451/watchdog_api.c
+++ b/targets/TARGET_NUVOTON/TARGET_M451/watchdog_api.c
@@ -99,6 +99,8 @@ watchdog_status_t hal_watchdog_init(const watchdog_config_t *config)
     if (! wdt_hw_inited) {
         wdt_hw_inited = 1;
 
+        SYS_UnlockReg();
+
         /* Enable IP module clock */
         CLK_EnableModuleClock(WDT_MODULE);
 
@@ -109,6 +111,8 @@ watchdog_status_t hal_watchdog_init(const watchdog_config_t *config)
         CLK_SetModuleClock(WDT_MODULE, CLK_CLKSEL1_WDTSEL_LIRC, 0);
 #endif
 
+        SYS_LockReg();
+
         /* Set up IP interrupt */
         NVIC_SetVector(WDT_IRQn, (uint32_t) WDT_IRQHandler);
         NVIC_EnableIRQ(WDT_IRQn);
diff --git a/targets/TARGET_NUVOTON/TARGET_M480/watchdog_api.c b/targets/TARGET_NUVOTON/TARGET_M480/watchdog_api.c
index 1016492a50..ae011649df 100644
--- a/targets/TARGET_NUVOTON/TARGET_M480/watchdog_api.c
+++ b/targets/TARGET_NUVOTON/TARGET_M480/watchdog_api.c
@@ -98,6 +98,8 @@ watchdog_status_t hal_watchdog_init(const watchdog_config_t *config)
     if (! wdt_hw_inited) {
         wdt_hw_inited = 1;
 
+        SYS_UnlockReg();
+
         /* Enable IP module clock */
         CLK_EnableModuleClock(WDT_MODULE);
 
@@ -108,6 +110,8 @@ watchdog_status_t hal_watchdog_init(const watchdog_config_t *config)
         CLK_SetModuleClock(WDT_MODULE, CLK_CLKSEL1_WDTSEL_LIRC, 0);
 #endif
 
+        SYS_LockReg();
+
         /* Set up IP interrupt */
         NVIC_SetVector(WDT_IRQn, (uint32_t) WDT_IRQHandler);
         NVIC_EnableIRQ(WDT_IRQn);
diff --git a/targets/TARGET_NUVOTON/TARGET_NANO100/watchdog_api.c b/targets/TARGET_NUVOTON/TARGET_NANO100/watchdog_api.c
index c0bc933cca..a058bd2d5b 100644
--- a/targets/TARGET_NUVOTON/TARGET_NANO100/watchdog_api.c
+++ b/targets/TARGET_NUVOTON/TARGET_NANO100/watchdog_api.c
@@ -101,12 +101,16 @@ watchdog_status_t hal_watchdog_init(const watchdog_config_t *config)
     if (! wdt_hw_inited) {
         wdt_hw_inited = 1;
 
+        SYS_UnlockReg();
+
         /* Enable IP module clock */
         CLK_EnableModuleClock(WDT_MODULE);
 
         /* Select IP clock source */
         CLK_SetModuleClock(WDT_MODULE, 0, 0);
 
+        SYS_LockReg();
+
         /* Set up IP interrupt */
         NVIC_SetVector(WDT_IRQn, (uint32_t) WDT_IRQHandler);
         NVIC_EnableIRQ(WDT_IRQn);
diff --git a/targets/TARGET_NUVOTON/TARGET_NUC472/watchdog_api.c b/targets/TARGET_NUVOTON/TARGET_NUC472/watchdog_api.c
index 529cd73244..9480a6ce79 100644
--- a/targets/TARGET_NUVOTON/TARGET_NUC472/watchdog_api.c
+++ b/targets/TARGET_NUVOTON/TARGET_NUC472/watchdog_api.c
@@ -98,6 +98,8 @@ watchdog_status_t hal_watchdog_init(const watchdog_config_t *config)
     if (! wdt_hw_inited) {
         wdt_hw_inited = 1;
 
+        SYS_UnlockReg();
+
         /* Enable IP module clock */
         CLK_EnableModuleClock(WDT_MODULE);
 
@@ -108,6 +110,8 @@ watchdog_status_t hal_watchdog_init(const watchdog_config_t *config)
         CLK_SetModuleClock(WDT_MODULE, CLK_CLKSEL1_WDTSEL_LIRC, 0);
 #endif
 
+        SYS_LockReg();
+
         /* Set up IP interrupt */
         NVIC_SetVector(WDT_IRQn, (uint32_t) WDT_IRQHandler);
         NVIC_EnableIRQ(WDT_IRQn);