220.127.116.11 Proper Assistant in Marriage of Eastern Catholics
1. For the validity of marriage, only a Latin priest and not a Latin deacon may witness a marriage if one or both parties are Eastern Catholics.  (The same hold true if one or both are Eastern non-Catholics, i.e., Orthdox, Oriental Orthodox, Assyrian Church of the East.)
 c. 1108 §3 (De Concordia Inter Codices); CCEO cc. 828 §§1-2, 832, §§1-3, IALP 82.