diff --git a/echo/aes_enc_round.h b/echo/aes_enc_round.h
index 18ffd9b..54bf6b0 100644
--- a/echo/aes_enc_round.h
+++ b/echo/aes_enc_round.h
@@ -20,11 +20,11 @@
 #ifndef AES_ENC_ROUND_H_
 #define AES_ENC_ROUND_H_
 
-typedef struct{
+typedef struct __attribute__((packed)) {
 	uint8_t s[16];
 } aes_cipher_state_t;
 
-typedef struct{
+typedef struct __attribute__((packed)) {
 	uint8_t ks[16];
 } aes_roundkey_t;