'Subquery returned more than 1 value' when updating a table that has a trigger

Question

I want to update 2 or more rows in a table with the same value:

UPDATE [dbo].[forms]
   SET [forExport] = 0

 WHERE (id = 4497 or id = 4496)

But I get back this error:

Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.