lib/PublicInbox/MsgIter.pm | 10 +++++++++-

diff --git a/lib/PublicInbox/MsgIter.pm b/lib/PublicInbox/MsgIter.pm
index e0127ab99de9478c78121eac03049de7fbd09f3b..ef0d209f6b391efc45ab843c3c8154a5cbd66557 100644
--- a/lib/PublicInbox/MsgIter.pm
+++ b/lib/PublicInbox/MsgIter.pm
@@ -7,6 +7,7 @@ use warnings;
 use base qw(Exporter);
 our @EXPORT = qw(msg_iter);
 use Email::MIME;
+use Scalar::Util qw(readonly);
 
 # Workaround Email::MIME versions without
 # commit dcef9be66c49ae89c7a5027a789bbbac544499ce
@@ -36,7 +37,14 @@ 				@sub = map { [ $_, $depth, @idx, ++$i ] } @sub;
 				@parts = (@sub, @parts);
 			} else {
 				if ($extra_nl) {
-					${$part->{body}} .= $part->{mycrlf};
+					my $lf = $part->{mycrlf};
+					my $bref = $part->{body};
+					if (readonly($$bref)) {
+						my $s = $$bref . $lf;
+						$part->{body} = \$s;
+					} else {
+						$$bref .= $lf;
+					}
 				}
 				$cb->($p);
 			}