diff --git a/library/aesce.h b/library/aesce.h
index 7048d77..61e73bf 100644
--- a/library/aesce.h
+++ b/library/aesce.h
@@ -52,6 +52,9 @@
 /**
  * \brief          Internal AES-ECB block encryption and decryption
  *
+ * Note: this assumes that the context specifies either 10, 12 or 14 rounds
+ * and will behave incorrectly if this is not the case.
+ *
  * \param ctx      AES context
  * \param mode     MBEDTLS_AES_ENCRYPT or MBEDTLS_AES_DECRYPT
  * \param input    16-byte input block