Nginx client_max_body_size can’t more than 2000m

just want to say, i can NOT reproduce this on nginx version 1.18.0:
setting

client_max_body_size 2000000000000M;

is accepted (this is 2 million terabytes, or 2 billion gigabytes)

however

client_max_body_size 20000000000000M;

is not accepted (this is 20 million terabytes, or 20 billion gigabytes) and i get the

nginx: [emerg] "client_max_body_size" directive invalid value in /etc/nginx/sites-enabled/files1.lan:23
nginx: configuration file /etc/nginx/nginx.conf test failed