t/perf-nntpd.t | 2 +-

diff --git a/t/perf-nntpd.t b/t/perf-nntpd.t
index 3ca1ce335768454dc4ea2f22f4d99912833474ee..ce3cc409b138e9ff751bea1f0f9955589f65ae70 100644
--- a/t/perf-nntpd.t
+++ b/t/perf-nntpd.t
@@ -108,7 +108,7 @@
 my $date = $ENV{NEWNEWS_DATE};
 unless ($date) {
 	my (undef, undef, undef, $d, $m, $y) = gmtime(time - 30 * 86400);
-	$date = sprintf('%04u%02u%02u', $y + 1900, $m, $d);
+	$date = sprintf('%04u%02u%02u', $y + 1900, $m + 1, $d);
 	diag "NEWNEWS_DATE undefined, using $date";
 }
 $t = timeit(1, sub {