diff --git a/psalm-baseline.xml b/psalm-baseline.xml
index d62d21a..4a8f159 100644
--- a/psalm-baseline.xml
+++ b/psalm-baseline.xml
@@ -1,15 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <files psalm-version="4.19.0@a2ad69ae4f5ab1f7d225a8dc4e2ec2d9415ed599">
   <file src="src/Event/WebhookEvent.php">
-    <FalsableReturnStatement occurrences="1">
-      <code>DateTimeImmutable::createFromFormat('U', (string) $this-&gt;received, new DateTimeZone('UTC'))</code>
-    </FalsableReturnStatement>
-    <InvalidFalsableReturnType occurrences="1">
-      <code>DateTimeImmutable</code>
-    </InvalidFalsableReturnType>
-    <MixedArgument occurrences="1">
-      <code>$serialized</code>
-    </MixedArgument>
     <MixedAssignment occurrences="2">
       <code>$this-&gt;payload</code>
       <code>$this-&gt;received</code>
diff --git a/src/Event/WebhookEvent.php b/src/Event/WebhookEvent.php
index 864b084..0e95cc3 100644
--- a/src/Event/WebhookEvent.php
+++ b/src/Event/WebhookEvent.php
@@ -6,6 +6,7 @@
 
 use DateTimeImmutable;
 use DateTimeZone;
+use Primo\Exception\RuntimeError;
 use Prismic\Json;
 use Serializable;
 
@@ -26,12 +27,17 @@ private function __construct(object $payload)
 
     public static function new(object $payload): self
     {
-        return new static($payload);
+        return new self($payload);
     }
 
     public function received(): DateTimeImmutable
     {
-        return DateTimeImmutable::createFromFormat('U', (string) $this->received, new DateTimeZone('UTC'));
+        $date = DateTimeImmutable::createFromFormat('U', (string) $this->received, new DateTimeZone('UTC'));
+        if ($date === false) {
+            throw new RuntimeError('Webhook event time evaluated to false');
+        }
+
+        return $date;
     }
 
     public function payload(): object
@@ -39,6 +45,9 @@ public function payload(): object
         return $this->payload;
     }
 
+    /**
+     * @deprecated
+     */
     public function serialize(): string
     {
         return Json::encode([
@@ -47,11 +56,37 @@ public function serialize(): string
         ]);
     }
 
-    /** @param mixed $serialized */
+    /**
+     * @deprecated
+     *
+     * @param string $serialized
+     *
+     * @phpcsSuppress SlevomatCodingStandard.TypeHints.ParameterTypeHint.MissingNativeTypeHint
+     */
     public function unserialize($serialized): void
     {
         $object = Json::decodeObject($serialized);
         $this->payload = $object->payload;
         $this->received = $object->received;
     }
+
+    /**
+     * @return array{received: int, payload: string}
+     */
+    public function __serialize(): array
+    {
+        return [
+            'received' => $this->received,
+            'payload' => Json::encode($this->payload),
+        ];
+    }
+
+    /**
+     * @param array{received: int, payload: string} $data
+     */
+    public function __unserialize(array $data): void
+    {
+        $this->received = $data['received'];
+        $this->payload = Json::decodeObject($data['payload']);
+    }
 }