diff --git a/include/mbedtls/cipher.h b/include/mbedtls/cipher.h
index 4a71383dd5..2d609db691 100644
--- a/include/mbedtls/cipher.h
+++ b/include/mbedtls/cipher.h
@@ -682,7 +682,7 @@ int mbedtls_cipher_reset( mbedtls_cipher_context_t *ctx );
  * \param ctx           The generic cipher context. This must be initialized.
  * \param ad            The additional data to use. This must be a readable
  *                      buffer of at least \p ad_len Bytes.
- * \param ad_len        The Length of \p ad Bytes.
+ * \param ad_len        The length of \p ad in Bytes.
  *
  * \return              \c 0 on success.
  * \return              A specific error code on failure.