Partitioning on the date part of a timestamp & PK issues

CREATE TABLE t (
    guid uuid not null,
    seq smallint not null,
    tid smallint not null,
    ts timestamp without time zone not null,
    x real,
    y real,
    z real,
    primary key (guid, tid, seq)
) partition by range (extract(date from ts));

Which results in the error:

ERROR:  unsupported PRIMARY KEY constraint with partition key definition
DETAIL:  PRIMARY KEY constraints cannot be used when partition keys include expressions.
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