diff --git a/tests/suites/test_suite_x509write.data b/tests/suites/test_suite_x509write.data
index 4eeeacd..0848550 100644
--- a/tests/suites/test_suite_x509write.data
+++ b/tests/suites/test_suite_x509write.data
@@ -184,5 +184,8 @@
 X509 String to Names #6 (Escape at end)
 mbedtls_x509_string_to_names:"C=NL, O=Offspark\\":"":MBEDTLS_ERR_X509_INVALID_NAME
 
+X509 String to Names #6 (Invalid, no '=' or ',')
+mbedtls_x509_string_to_names:"ABC123":"":MBEDTLS_ERR_X509_INVALID_NAME
+
 Check max serial length
 x509_set_serial_check: