parallel pg_dump causes assertion failure in HEAD

$ pg_dump -F d -j 4 -f foo regression
pg_dump: [archiver (db)] query failed: pg_dump: [parallel archiver] query was: SET TRANSACTION SNAPSHOT '00002130-1'
pg_dump: [archiver (db)] query failed: pg_dump: [archiver (db)] query failed: pg_dump: [archiver (db)] query failed: $

postmaster log shows:

TRAP: FailedAssertion("!(HistoricSnapshotActive())", File: "snapmgr.c", Line: 355)
TRAP: FailedAssertion("!(HistoricSnapshotActive())", File: "snapmgr.c", Line: 355)
TRAP: FailedAssertion("!(HistoricSnapshotActive())", File: "snapmgr.c", Line: 355)
TRAP: FailedAssertion("!(HistoricSnapshotActive())", File: "snapmgr.c", Line: 355)
LOG:  server process (PID 15069) was terminated by signal 6: Aborted
DETAIL:  Failed process was running: SET TRANSACTION SNAPSHOT '00002130-1'
LOG:  terminating any other active server processes

That Assert appears to have been introduced by commit b89e1510.
        regards, tom lane