diff --git a/core/lib/aes-128.c b/core/lib/aes-128.c
index 473adf6fc..59b16421e 100644
--- a/core/lib/aes-128.c
+++ b/core/lib/aes-128.c
@@ -80,7 +80,7 @@ galois_mul2(uint8_t value)
 }
 /*---------------------------------------------------------------------------*/
 static void
-set_key(uint8_t *key)
+set_key(const uint8_t *key)
 {
   uint8_t i;
   uint8_t j;
diff --git a/core/lib/aes-128.h b/core/lib/aes-128.h
index a16155b4f..59a7f7c33 100644
--- a/core/lib/aes-128.h
+++ b/core/lib/aes-128.h
@@ -59,7 +59,7 @@ struct aes_128_driver {
   /**
    * \brief Sets the current key.
    */
-  void (* set_key)(uint8_t *key);
+  void (* set_key)(const uint8_t *key);
   
   /**
    * \brief Encrypts.