diff --git a/targets/TARGET_NUVOTON/TARGET_M2351/device/m2351_stddriver_sup.c b/targets/TARGET_NUVOTON/TARGET_M2351/device/m2351_stddriver_sup.c
index 258bc31dbf..56011319e3 100644
--- a/targets/TARGET_NUVOTON/TARGET_M2351/device/m2351_stddriver_sup.c
+++ b/targets/TARGET_NUVOTON/TARGET_M2351/device/m2351_stddriver_sup.c
@@ -181,6 +181,22 @@ void CLK_DisableModuleClock_S(uint32_t u32ModuleIndex)
     CLK_DisableModuleClock(u32ModuleIndex);
 }
 
+__NONSECURE_ENTRY
+void SYS_LockReg_S(void)
+{
+    /* Allow non-secure domain to lock/unlock locked registers without check.
+     * Guard access to locked registers is done through other related secure functions. */
+    SYS_LockReg();
+}
+
+__NONSECURE_ENTRY
+void SYS_UnlockReg_S(void)
+{
+    /* Allow non-secure domain to lock/unlock locked registers without check.
+     * Guard access to locked registers is done through other related secure functions. */
+    SYS_UnlockReg();
+}
+
 static bool check_mod_ns(int modclass, uint32_t modidx)
 {
     const nu_modidx_ns_t *modidx_ns = modidx_ns_tab;
diff --git a/targets/TARGET_NUVOTON/TARGET_M2351/device/m2351_stddriver_sup.h b/targets/TARGET_NUVOTON/TARGET_M2351/device/m2351_stddriver_sup.h
index 8d2d43b9bf..ecf2993292 100644
--- a/targets/TARGET_NUVOTON/TARGET_M2351/device/m2351_stddriver_sup.h
+++ b/targets/TARGET_NUVOTON/TARGET_M2351/device/m2351_stddriver_sup.h
@@ -51,6 +51,20 @@ void CLK_EnableModuleClock_S(uint32_t u32ModuleIndex);
  */
 void CLK_DisableModuleClock_S(uint32_t u32ModuleIndex);
 
+/* Secure SYS_LockReg
+ *
+ * Guard access to secure module from non-secure domain before SYS_LockReg.
+ * Its synopsis is the same as SYS_LockReg.
+ */
+void SYS_LockReg_S(void);
+
+/* Secure SYS_UnlockReg
+ *
+ * Guard access to secure module from non-secure domain before SYS_UnlockReg.
+ * Its synopsis is the same as SYS_UnlockReg.
+ */
+void SYS_UnlockReg_S(void);
+
 #ifdef __cplusplus
 }
 #endif