Cannot use flock with mocked file

[atoomic]

When mocking a file using Test::MockFile, flock is failing

use Test::MockFile;
use Fcntl;

my $f = q[/tmp/myfile];
my $mocked = Test::MockFile->file( $f => q[content] );

open( my $fh, '>', $f ) or die;
flock( $fh, Fcntl::LOCK_EX() | Fcntl::LOCK_NB() ) or die $!;

output

flock() on unopened filehandle GEN0 at t.pl line 12.
Bad file descriptor at t.pl line 12.