diff --git a/src/Activities/ValidationHandler.php b/src/Activities/ValidationHandler.php
index 2042ebb..f5d57fa 100644
--- a/src/Activities/ValidationHandler.php
+++ b/src/Activities/ValidationHandler.php
@@ -28,25 +28,31 @@ class ValidationHandler implements EventSubscriberInterface
     public function verifyInboxActivity( InboxActivityEvent $event )
     {
         $activity = $event->getActivity();
-        $this->requireFields( $activity, array( 'type', 'id', 'actor' ) );
-        if ( in_array( $activity['type'], self::OBJECT_REQUIRED_TYPES ) ) {
-            $this->requireFields( $activity, array( 'object' ) );
+        $requiredFields = array( 'type', 'id', 'actor' );
+        if ( array_key_exists( 'type', $activity ) &&
+             in_array( $activity['type'], self::OBJECT_REQUIRED_TYPES ) ) {
+            $requiredFields[] = 'object';
         }
-        if ( in_array( $activity['type'], self::TARGET_REQUIRED_TYPES ) ) {
-            $this->requireFields( $activity, array( 'target' ) );
+        if ( array_key_exists( 'type', $activity ) &&
+             in_array( $activity['type'], self::TARGET_REQUIRED_TYPES ) ) {
+            $requiredFields[] = 'target';
         }
+        $this->requireFields( $activity, $requiredFields );
     }
 
     public function verifyOutboxActivity( OutboxActivityEvent $event )
     {
         $activity = $event->getActivity();
-        $this->requireFields( $activity, array( 'type' ) );
-        if ( in_array( $activity['type'], self::OBJECT_REQUIRED_TYPES ) ) {
-            $this->requireFields( $activity, array( 'object' ) );
+        $requiredFields = array( 'type', 'actor' );
+        if ( array_key_exists( 'type', $activity ) &&
+             in_array( $activity['type'], self::OBJECT_REQUIRED_TYPES ) ) {
+            $requiredFields[] = 'object';
         }
-        if ( in_array( $activity['type'], self::TARGET_REQUIRED_TYPES ) ) {
-            $this->requireFields( $activity, array( 'target' ) );
+        if ( array_key_exists( 'type', $activity ) &&
+             in_array( $activity['type'], self::TARGET_REQUIRED_TYPES ) ) {
+            $requiredFields[] = 'target';
         }
+        $this->requireFields( $activity, $requiredFields );
     }
 
     private function requireFields( array $activity, array $fields )
diff --git a/test/Activities/ValidationHandlerTest.php b/test/Activities/ValidationHandlerTest.php
index c5265a5..a494c80 100644
--- a/test/Activities/ValidationHandlerTest.php
+++ b/test/Activities/ValidationHandlerTest.php
@@ -52,7 +52,7 @@ class ValidationHandlerTest extends TestCase
                     Request::create( 'https://example.com' )
                 ),
                 'expectedException' => BadRequestHttpException::class,
-                'expectedExceptionMessage' => 'Missing activity fields: type',
+                'expectedExceptionMessage' => 'Missing activity fields: type,actor',
             ),
             array(
                 'id' => 'inboxPassesValidActivity',
@@ -79,6 +79,7 @@ class ValidationHandlerTest extends TestCase
                 'event' => new OutboxActivityEvent(
                     array(
                         'type' => 'Create',
+                        'actor' => 'https://example.com/actor/1',
                         'object' => array(
                             'type' => 'Note',
                         ),
@@ -96,6 +97,7 @@ class ValidationHandlerTest extends TestCase
                 'event' => new OutboxActivityEvent(
                     array(
                         'type' => 'Create',
+                        'actor' => 'https://example.com/actor/1',
                     ),
                     TestActivityPubObject::fromArray( array(
                         'id' => 'https://example.com/actor/1',
@@ -144,9 +146,10 @@ class ValidationHandlerTest extends TestCase
                 'event' => new OutboxActivityEvent(
                     array(
                         'type' => 'Remove',
+                        'actor' => 'https://example.com/actor/1',
                     ),
                     TestActivityPubObject::fromArray( array(
-                        'id' => 'https://notexample.com/actor/1',
+                        'id' => 'https://example.com/actor/1',
                         'type' => 'Person',
                     ) ),
                     Request::create( 'https://example.com' )