diff --git a/lib/hx509/cert.c b/lib/hx509/cert.c
index ebf02a99e..452bd0ecd 100644
--- a/lib/hx509/cert.c
+++ b/lib/hx509/cert.c
@@ -3251,7 +3251,7 @@ _hx509_cert_get_eku(hx509_context context,
  * @param context A hx509 context.
  * @param c the certificate to encode.
  * @param os the encode certificate, set to NULL, 0 on case of
- * error. Free the returned structure with hx509_xfree().
+ * error. Free the os->data with hx509_xfree().
  *
  * @return An hx509 error code, see hx509_get_error_string().
  *