--- a/t/dates.t
+++ b/t/dates.t
@@ -37,7 +37,7 @@
 {
 	no warnings 'once';
 	local $::main::QueueID = 'wookie';
-	like(::main::gen_msgid_header(), qr/Message-ID: <\d{12}\.wookie\@[-a-zA-Z0-9\.]+>\n/, 'Got Message-ID header in correct format');
+	like(::main::gen_msgid_header(), qr/Message-ID: <\d{12}\.wookie\@[-_a-zA-Z0-9\.]+>\n/, 'Got Message-ID header in correct format');
 }
 
 sub t_time_str: Test(1)