pg_dump: ERROR: array size exceeds the maximum allowed (268435455)

Hello,
I'm trying to save a database from a dying disk on a Gentoo/Linux box.
Unfortunately, when I'm issuing a
$ pg_dumpall --clean
I got

pg_dump: [programme d'archivage (db)] échec de la requête : ERROR:  array size exceeds the maximum allowed (268435455)
pg_dump: [programme d'archivage (db)] la requête était : SELECT p.tableoid, p.oid, p.proname AS aggname, p.pronamespace AS aggnamespace, p.pronargs, p.proargtypes, (SELECT rolname FROM pg_catalog.pg_roles WHERE oid = p.proowner) AS rolname, (SELECT pg_catalog.array_agg(acl ORDER BY row_n) FROM (SELECT acl, row_n FROM pg_catalog.unnest(coalesce(p.proacl,pg_catalog.acldefault('f',p.proowner))) WITH ORDINALITY AS perm(acl,row_n) WHERE NOT EXISTS ( SELECT 1 FROM pg_catalog.unnest(coalesce(pip.initprivs,pg_catalog.acldefault('f',p.proowner))) AS init(init_acl) WHERE acl = init_acl)) as foo) AS aggacl, (SELECT pg_catalog.array_agg(acl ORDER BY row_n) FROM (SELECT acl, row_n FROM pg_catalog.unnest(coalesce(pip.initprivs,pg_catalog.acldefault('f',p.proowner))) WITH ORDINALITY AS initp(acl,row_n) WHERE NOT EXISTS ( SELECT 1 FROM pg_catalog.unnest(coalesce(p.proacl,pg_catalog.acldefault('f',p.proowner))) AS permp(orig_acl) WHERE acl = orig_acl)) as foo) AS raggacl, NULL AS initaggacl, NULL AS initraggacl FROM pg_proc p LEFT JOIN pg_init_privs pip ON (p.oid = pip.objoid AND pip.classoid = 'pg_proc'::regclass AND pip.objsubid = 0) WHERE p.proisagg AND (p.pronamespace != (SELECT oid FROM pg_namespace WHERE nspname = 'pg_catalog') OR p.proacl IS DISTINCT FROM pip.initprivs)
pg_dumpall : échec de pg_dump sur la base de données « postgres », quitte

All references I found about this error is about user made request.Any clue to how I can correct this issue ? (as said, my disk is dying due to its controller failure so, obviously time is running :) ).This database contains my smart home figures so nothing critical and I have a "weeks old" backup.
This box is running
    pg_dump (PostgreSQL) 10.3
but I was on way to upgrade to 10.6 when I discovered this issue.
Best regards,
Laurent