diff --git a/include/polarssl/cipher.h b/include/polarssl/cipher.h
index 5789f77..853c7e6 100644
--- a/include/polarssl/cipher.h
+++ b/include/polarssl/cipher.h
@@ -55,6 +55,7 @@
 #define POLARSSL_ERR_CIPHER_ALLOC_FAILED                   -0x6180  /**< Failed to allocate memory. */
 #define POLARSSL_ERR_CIPHER_INVALID_PADDING                -0x6200  /**< Input data contains invalid padding and is rejected. */
 #define POLARSSL_ERR_CIPHER_FULL_BLOCK_EXPECTED            -0x6280  /**< Decryption of block requires a full block. */
+#define POLARSSL_ERR_CIPHER_AUTH_FAILED                    -0x6300  /**< Authentication failed (for AEAD modes). */
 
 #ifdef __cplusplus
 extern "C" {