postrges on conflict update with all columns as unique constraint

I have a table with columns 'id', 'a', 'b, 'c', 'd'. Also, I have a unique constraint on ('a', 'b', 'c', 'd') so no entries can be added where all those fields are the same. I want to upsert entries e.g. I have in db: 1 a_value b_value c_value d_value and I'm upserting INSERT INTO MYTABLE(a, b, c, d) values ('a_value', 'b_value', 'c_value', 'd_value__new') on conflict (a, b, c, d) DO UPDATE SET d= excluded.d; But this creates new entry when I expected that it will update d_value to d_value_new on existing entry. What am I doing wrong? See example here: https://dbfiddle.uk/nL7fRpt_