diff --git a/library/aes.c b/library/aes.c
index a1d8f86..9f75f20 100644
--- a/library/aes.c
+++ b/library/aes.c
@@ -183,6 +183,7 @@
 
 #undef FT
 
+#if !(defined(MBEDTLS_AES_SETKEY_ENC_ALT) && defined(MBEDTLS_AES_DECRYPT_ALT))
 /*
  * Reverse S-box
  */
@@ -221,6 +222,7 @@
     0x17, 0x2B, 0x04, 0x7E, 0xBA, 0x77, 0xD6, 0x26,
     0xE1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0C, 0x7D
 };
+#endif /* !(defined(MBEDTLS_AES_SETKEY_ENC_ALT) && defined(MBEDTLS_AES_DECRYPT_ALT)) */
 
 /*
  * Reverse tables
@@ -340,7 +342,9 @@
 /*
  * Reverse S-box & tables
  */
+#if !(defined(MBEDTLS_AES_SETKEY_ENC_ALT) && defined(MBEDTLS_AES_DECRYPT_ALT))
 static unsigned char RSb[256];
+#endif
 static uint32_t RT0[256];
 #if !defined(MBEDTLS_AES_FEWER_TABLES)
 static uint32_t RT1[256];