diff --git a/aes.c b/aes.c
index 38ec132..d44d281 100644
--- a/aes.c
+++ b/aes.c
@@ -434,7 +434,7 @@ static void InvCipher(void)
   AddRoundKey(0);
 }
 
-static void BlockCopy(uint8_t* output, uint8_t* input)
+static void BlockCopy(uint8_t* output, const uint8_t* input)
 {
   uint8_t i;
   for (i=0;i<KEYLEN;++i)
@@ -451,7 +451,7 @@ static void BlockCopy(uint8_t* output, uint8_t* input)
 #if defined(ECB) && ECB
 
 
-void AES128_ECB_encrypt(uint8_t* input, const uint8_t* key, uint8_t* output)
+void AES128_ECB_encrypt(const uint8_t* input, const uint8_t* key, uint8_t* output)
 {
   // Copy input to output, and work in-memory on output
   BlockCopy(output, input);
@@ -464,7 +464,7 @@ void AES128_ECB_encrypt(uint8_t* input, const uint8_t* key, uint8_t* output)
   Cipher();
 }
 
-void AES128_ECB_decrypt(uint8_t* input, const uint8_t* key, uint8_t *output)
+void AES128_ECB_decrypt(const uint8_t* input, const uint8_t* key, uint8_t *output)
 {
   // Copy input to output, and work in-memory on output
   BlockCopy(output, input);
diff --git a/aes.h b/aes.h
index 708a09c..e86ab7f 100644
--- a/aes.h
+++ b/aes.h
@@ -22,8 +22,8 @@
 
 #if defined(ECB) && ECB
 
-void AES128_ECB_encrypt(uint8_t* input, const uint8_t* key, uint8_t *output);
-void AES128_ECB_decrypt(uint8_t* input, const uint8_t* key, uint8_t *output);
+void AES128_ECB_encrypt(const uint8_t* input, const uint8_t* key, uint8_t *output);
+void AES128_ECB_decrypt(const uint8_t* input, const uint8_t* key, uint8_t *output);
 
 #endif // #if defined(ECB) && ECB