-uschar txt[256];
-size_t sz = sizeof(txt);
-return ( gnutls_x509_crt_get_issuer_dn(cert, CS txt, &sz) == 0 )
- ? string_copy(txt) : NULL;
+uschar * cp = NULL;
+int ret;
+size_t siz = 0;
+
+if ((ret = gnutls_x509_crt_get_issuer_dn(cert, cp, &siz))
+ != GNUTLS_E_SHORT_MEMORY_BUFFER)
+ return g_err("gi0", __FUNCTION__, ret);
+
+cp = store_get(siz);
+if ((ret = gnutls_x509_crt_get_issuer_dn(cert, cp, &siz)) < 0)
+ return g_err("gi1", __FUNCTION__, ret);
+
+return mod ? tls_field_from_dn(cp, mod) : cp;