Texas passed an amendment in 2005 with the intent of banning gay-marriage. But they may have banned more than they intended.
The amendment contains the text:
This state or a political subdivision of this state may not create or recognize any legal status identical or similar to marriage.
Logically, it seems like “marriage” is a member of the set of legal statuses “identical or similar to marriage”. Of course, there’s no telling how a judge would interpret the idea of something being “identical or similar” to itself.