invalid memory alloc request size from pg_stat_activity?

Hello,

We're upgrading from postgresql 9.6 to 10.6 and everything is working fine, but any query against pg_stat_activity
resultsin ERROR:  invalid memory alloc request size 1652113408 

e.g:

ourdb=> SELECT pid, state, age(query_start, clock_timestamp()), usename, query FROM pg_stat_activity WHERE query !=
'<IDLE>'AND state != 'idle' ORDER BY age limit 100; 
ERROR:  invalid memory alloc request size 1652113408

Maybe this has to do with us setting track_activity_query_size=102400? Is there a known safe maximum for that, or could
therebe some other problem? 

Thanks,
James