dependent => destroy on has_one not working

I must be overlooking something simple.

I have two models. They have a has_one association. I am trying to destroy the child has_one association but it's not working.

class Column
  has_one :subtable, :class_name => "Table", :foreign_key => :parent_id, :dependent => :destroy
end

// the parent_id column is on the `table` table
class Table
  belongs_to :parent_column, :class_name => "Column", :foreign_key => :parent_id
end

If I do

@column.destroy

The table doesn't get destroyed. What am I missing?