diff --git a/aes.h b/aes.h
index f4ed03c..eae5bb2 100644
--- a/aes.h
+++ b/aes.h
@@ -3,7 +3,7 @@
 
 #include <stdint.h>
 
-void AES128_ECB_encrypt(uint8_t* input, uint8_t* key, uint8_t *output);
-void AES128_ECB_decrypt(uint8_t* input, uint8_t* key, uint8_t *output);
+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);
 
 #endif //_AES_H_