-exim_datum_data_set(&key, string_copyn(keystring, length));
-exim_datum_size_set(&key, length + 1);
+length++;
+exim_datum_data_set(&key,
+ memcpy(store_get(length, keystring), keystring, length)); /* key can have embedded NUL */
+exim_datum_size_set(&key, length);