diff --git a/library/x509_create.c b/library/x509_create.c
index 6483b39..99115c4 100644
--- a/library/x509_create.c
+++ b/library/x509_create.c
@@ -274,7 +274,7 @@
         if (in_attr_type && *c == '=') {
             if ((attr_descr = x509_attr_descr_from_name(s, c - s)) == NULL) {
                 if ((oid = x509_oid_from_numericoid(s, c - s)) == NULL) {
-                    return MBEDTLS_ERR_X509_UNKNOWN_OID;
+                    return MBEDTLS_ERR_X509_INVALID_NAME;
                 } else {
                     numericoid = 1;
                 }