lib/PublicInbox/LeiMailDiff.pm | 1 -

diff --git a/lib/PublicInbox/LeiMailDiff.pm b/lib/PublicInbox/LeiMailDiff.pm
index b21a0c366fd68aa6c8198a99e7bbf5b7f9ea8cca..48ba74cfe886f1811aa078670491ebce8f44eb09 100644
--- a/lib/PublicInbox/LeiMailDiff.pm
+++ b/lib/PublicInbox/LeiMailDiff.pm
@@ -76,7 +76,6 @@ }
 
 sub lei_mail_diff {
 	my ($lei, @argv) = @_;
-	$lei->{opt}->{'in-format'} //= 'eml' if !grep(/\A[a-z0-9]+:/i, @argv);
 	my $self = bless {}, __PACKAGE__;
 	$self->prepare_inputs($lei, \@argv) or return;
 	my $isatty = -t $lei->{1};