look for the definition of 'wife'. It would be unusual if it said wife rather than 'spouse' so look carefully.
Perhaps it is an older deed, drafted in a time when people got married.
If the defacto does not fall under the definition then you have 2 choices
1. amend the deed or
2. marry the defacto
actually there are more choices
3. don't distribute to her/him
4. distribute to a related trust which may also be a beneficiary
Seek advice before doing any of the above.