diff --git a/include/mbedtls/cipher.h b/include/mbedtls/cipher.h
index 6ce82a3..c04097d 100644
--- a/include/mbedtls/cipher.h
+++ b/include/mbedtls/cipher.h
@@ -515,6 +515,7 @@
  *
  * \return      The recommended IV size.
  * \return      \c 0 for ciphers not using an IV or a nonce.
+ * \return      \c 0 if \p info is \c NULL.
  */
 static inline size_t mbedtls_cipher_info_get_iv_size(
     const mbedtls_cipher_info_t *info )