lib/PublicInbox/ContentId.pm | 9 +++------

diff --git a/lib/PublicInbox/ContentId.pm b/lib/PublicInbox/ContentId.pm
index eb937a0e722982937f4a93619c00330f7b4d15b2..0c4a8678beb02fa4db436ca12c55eda6bc0edc79 100644
--- a/lib/PublicInbox/ContentId.pm
+++ b/lib/PublicInbox/ContentId.pm
@@ -60,12 +60,9 @@
 	# References: and In-Reply-To: get used interchangeably
 	# in some "duplicates" in LKML.  We treat them the same
 	# in SearchIdx, so treat them the same for this:
-	my %seen;
-	foreach my $mid (@{mids($hdr)}) {
-		# do NOT consider the Message-ID as part of the content_id
-		# if we got here, we've already got Message-ID reuse
-		$seen{$mid} = 1;
-	}
+	# do NOT consider the Message-ID as part of the content_id
+	# if we got here, we've already got Message-ID reuse
+	my %seen = map { $_ => 1 } @{mids($hdr)};
 	foreach my $mid (@{references($hdr)}) {
 		next if $seen{$mid};
 		$dig->add("ref\0$mid\0");