diff --git a/core/app/Ingest/DueAtParser.php b/core/app/Ingest/DueAtParser.php
index af08256..96eaa6e 100644
--- a/core/app/Ingest/DueAtParser.php
+++ b/core/app/Ingest/DueAtParser.php
@@ -10,7 +10,7 @@ final class DueAtParser
 {
     private const DATE = '/^(\d{4})-(\d{2})-(\d{2})$/';
     private const LOCAL_DATETIME = '/^(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2})(?::(\d{2}))?$/';
-    private const FIXED_DATETIME = '/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}(?::\d{2})?(Z|[+-]\d{2}:\d{2})$/';
+    private const FIXED_DATETIME = '/^(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2})(?::(\d{2}))?(Z|[+-]\d{2}:\d{2})$/';
 
     public static function parse(string $raw): ParsedDue
     {
@@ -30,7 +30,10 @@ final class DueAtParser
             );
         }
 
-        if (preg_match(self::FIXED_DATETIME, $raw)) {
+        if (preg_match(self::FIXED_DATETIME, $raw, $m)) {
+            self::assertDate((int) $m[1], (int) $m[2], (int) $m[3], $raw);
+            self::assertTime((int) $m[4], (int) $m[5], (int) ($m[6] ?? 0), $raw);
+
             try {
                 return ParsedDue::fixed(CarbonImmutable::parse($raw));
             } catch (\Throwable $e) {
diff --git a/core/tests/Unit/Ingest/DueAtParserTest.php b/core/tests/Unit/Ingest/DueAtParserTest.php
index 335ce9c..2753526 100644
--- a/core/tests/Unit/Ingest/DueAtParserTest.php
+++ b/core/tests/Unit/Ingest/DueAtParserTest.php
@@ -43,7 +43,7 @@ class DueAtParserTest extends TestCase
 
     public function test_garbage_is_rejected(): void
     {
-        foreach (['', 'tomorrow', '2026-13-01', '14:00', '2026-09-10 14:00', '2026-09-10T25:00'] as $bad) {
+        foreach (['', 'tomorrow', '2026-13-01', '14:00', '2026-09-10 14:00', '2026-09-10T25:00', '2026-02-30T08:15:00+02:00', '2026-09-10T25:00Z'] as $bad) {
             try {
                 DueAtParser::parse($bad);
                 $this->fail("accepted: $bad");