diff --git a/targets/TARGET_NUVOTON/TARGET_M480/crypto/crypto-misc.h b/targets/TARGET_NUVOTON/TARGET_M480/crypto/crypto-misc.h
index 1527a59c6d..4bee4f644c 100644
--- a/targets/TARGET_NUVOTON/TARGET_M480/crypto/crypto-misc.h
+++ b/targets/TARGET_NUVOTON/TARGET_M480/crypto/crypto-misc.h
@@ -35,6 +35,8 @@ extern volatile int g_AES_done;
 void crypto_init(void);
 void crypto_uninit(void);
 
+/* Clear buffer to zero
+ * Implementation that should never be optimized out by the compiler */
 void crypto_zeroize(void *v, size_t n);
 
 /* Acquire/release ownership of AES H/W */
diff --git a/targets/TARGET_NUVOTON/TARGET_NUC472/crypto/crypto-misc.h b/targets/TARGET_NUVOTON/TARGET_NUC472/crypto/crypto-misc.h
index 1527a59c6d..4bee4f644c 100644
--- a/targets/TARGET_NUVOTON/TARGET_NUC472/crypto/crypto-misc.h
+++ b/targets/TARGET_NUVOTON/TARGET_NUC472/crypto/crypto-misc.h
@@ -35,6 +35,8 @@ extern volatile int g_AES_done;
 void crypto_init(void);
 void crypto_uninit(void);
 
+/* Clear buffer to zero
+ * Implementation that should never be optimized out by the compiler */
 void crypto_zeroize(void *v, size_t n);
 
 /* Acquire/release ownership of AES H/W */