ASN1C provides some support for the old X.208 version of the standard through the -asnstd x208 command-line option.

ASN1C when used with this option contains extensions to handle the older, now withdrawn version of ASN.1. Although this version is no longer supported by the ITU-T, it is still in use today.

This version of the compiler also contains logic to parse some common MACRO definitions that are still in widespread use despite the fact that MACRO syntax was retired with this version of the standard. The types of MACRO definitions that are supported are ROSE OPERATION and ERROR and SNMP OBJECT-TYPE.