diff --git a/libavutil/xtea.h b/libavutil/xtea.h
index bcf786cce3..06f5a2f470 100644
--- a/libavutil/xtea.h
+++ b/libavutil/xtea.h
@@ -45,12 +45,14 @@ AVXTEA *av_xtea_alloc(void);
  * Initialize an AVXTEA context.
  *
  * @param ctx an AVXTEA context
- * @param key a key of 16 bytes used for encryption/decryption
+ * @param key a key of 16 bytes used for encryption/decryption,
+ *            interpreted as big endian 32 bit numbers
  */
 void av_xtea_init(struct AVXTEA *ctx, const uint8_t key[16]);
 
 /**
- * Encrypt or decrypt a buffer using a previously initialized context.
+ * Encrypt or decrypt a buffer using a previously initialized context,
+ * in big endian format.
  *
  * @param ctx an AVXTEA context
  * @param dst destination array, can be equal to src