diff --git a/lib/Lacuna/RPC/Building/SpacePort.pm b/lib/Lacuna/RPC/Building/SpacePort.pm
index 6afa95ce..fa76b894 100644
--- a/lib/Lacuna/RPC/Building/SpacePort.pm
+++ b/lib/Lacuna/RPC/Building/SpacePort.pm
@@ -248,6 +248,11 @@ sub find_arrival {
     my $now     = DateTime->now;
     my $year = $arrival_params->{year} ? $arrival_params->{year} : $now->year;
     my $month = $arrival_params->{month} ? $arrival_params->{month} : $now->month;
+
+    if ($month < 1 or 12 < $month) {
+        confess [1002, 'Invalid month'];
+    }
+
     my $mon_end = DateTime->last_day_of_month(year => $year, month => $month);
     my $day     = $arrival_params->{day};
     my $hour    = $arrival_params->{hour};
diff --git a/var/www/public/changes.txt b/var/www/public/changes.txt
index a2114560..1ff8acd9 100644
--- a/var/www/public/changes.txt
+++ b/var/www/public/changes.txt
@@ -1,6 +1,7 @@
 3.0917:
  - Fix: Recalc stats when building 1+x plans.
  - Fix: Station incoming shows your incoming as own, not station owner's incoming.
+ - Fix: Better input validation for fleet.
 
 3.0916:
  - Mod: Jackpot enhanced.