diff --git a/targets/TARGET_NUVOTON/TARGET_M480/crypto/crypto-misc.c b/targets/TARGET_NUVOTON/TARGET_M480/crypto/crypto-misc.c
index 8f2aed1509..87af3a9271 100644
--- a/targets/TARGET_NUVOTON/TARGET_M480/crypto/crypto-misc.c
+++ b/targets/TARGET_NUVOTON/TARGET_M480/crypto/crypto-misc.c
@@ -104,7 +104,7 @@ void crypto_uninit(void)
 /* Implementation that should never be optimized out by the compiler */
 void crypto_zeroize(void *v, size_t n)
 {
-    volatile unsigned char *p = (unsigned char*) v;
+    volatile unsigned char *p = (volatile unsigned char*) v;
     while (n--) {
         *p++ = 0;
     }
@@ -113,7 +113,7 @@ void crypto_zeroize(void *v, size_t n)
 /* Implementation that should never be optimized out by the compiler */
 void crypto_zeroize32(uint32_t *v, size_t n)
 {
-    volatile uint32_t *p = (uint32_t*) v;
+    volatile uint32_t *p = (volatile uint32_t*) v;
     while (n--) {
         *p++ = 0;
     }
diff --git a/targets/TARGET_NUVOTON/TARGET_NUC472/crypto/crypto-misc.c b/targets/TARGET_NUVOTON/TARGET_NUC472/crypto/crypto-misc.c
index 72581362d7..c9cdc1098e 100644
--- a/targets/TARGET_NUVOTON/TARGET_NUC472/crypto/crypto-misc.c
+++ b/targets/TARGET_NUVOTON/TARGET_NUC472/crypto/crypto-misc.c
@@ -100,7 +100,7 @@ void crypto_uninit(void)
 /* Implementation that should never be optimized out by the compiler */
 void crypto_zeroize(void *v, size_t n)
 {
-    volatile unsigned char *p = (unsigned char*) v;
+    volatile unsigned char *p = (volatile unsigned char*) v;
     while (n--) {
         *p++ = 0;
     }