diff --git a/includes/activitypub/collection/class-event-sources.php b/includes/activitypub/collection/class-event-sources.php
index 649a683..f01ff5e 100644
--- a/includes/activitypub/collection/class-event-sources.php
+++ b/includes/activitypub/collection/class-event-sources.php
@@ -245,34 +245,28 @@ class Event_Sources {
 	 * @return void
 	 */
 	public static function delete_events_by_event_source( $event_source_id ) {
-		$args = array(
-			'author'         => 0, // Currently we do not use a special user or special users.
-			'posts_per_page' => -1, // Retrieve all matching posts.
-			'meta_key'       => '_event_bridge_for_activitypub_event_source',
-			'meta_query'     => array(
-				array(
-					'key'     => '_event_bridge_for_activitypub_event_source',
-					'value'   => $event_source_id,
-					'compare' => '=',
-				),
-			),
+		global $wpdb;
+		$results = $wpdb->get_results(
+			$wpdb->prepare(
+				"SELECT * FROM $wpdb->postmeta WHERE meta_key = %s AND meta_value = %s",
+				'_event_bridge_for_activitypub_event_source',
+				esc_sql( $event_source_id )
+			)
 		);
 
-		$query = new \WP_Query( $args );
-
 		// If no matching posts are found, return early.
-		if ( ! $query->have_posts() ) {
+		if ( empty( $results ) || ! $results ) {
 			return;
 		}
 
 		// Loop through the posts and delete them permanently.
-		foreach ( $query->posts as $post ) {
+		foreach ( $results as $post ) {
 			// Check if the post has a thumbnail.
-			$thumbnail_id = get_post_thumbnail_id( $post->ID );
+			$thumbnail_id = get_post_thumbnail_id( $post->post_id );
 
 			if ( $thumbnail_id ) {
 				// Remove the thumbnail from the post.
-				\delete_post_thumbnail( $post->ID );
+				\delete_post_thumbnail( $post->post_id  );
 
 				// Delete the attachment (and its files) from the media library.
 				if ( self::is_attachment_featured_image( $thumbnail_id ) ) {
@@ -280,7 +274,7 @@ class Event_Sources {
 				}
 			}
 
-			\wp_delete_post( $post->ID, true );
+			\wp_delete_post( $post->post_id , true );
 		}
 
 		// Clean up the query.
diff --git a/tests/includes/class-test-event-sources.php b/tests/includes/class-test-event-sources.php
index 32f3cf8..8918c2e 100644
--- a/tests/includes/class-test-event-sources.php
+++ b/tests/includes/class-test-event-sources.php
@@ -30,6 +30,15 @@ class Test_Event_Sources extends \WP_UnitTestCase {
 		'summary' => 'Just a random organizer of events in the Fediverse',
 	);
 
+	const FOLLOWED_ACTOR_2 = array(
+		'id'      => 'https://remote.example/@organizer2',
+		'type'    => 'Person',
+		'inbox'   => 'https://remote.example/@organizer2/inbox',
+		'outbox'  => 'https://remote.example/@organizer2/outbox',
+		'name'    => 'The Second Organizer',
+		'summary' => 'Just a second random organizer of events in the Fediverse',
+	);
+
 	/**
 	 * REST Server.
 	 *
@@ -312,4 +321,96 @@ class Test_Event_Sources extends \WP_UnitTestCase {
 
 		\remove_filter( 'activitypub_defer_signature_verification', '__return_true' );
 	}
+
+	/**
+	 * Test receiving "Accept" of "Follow".
+	 */
+	public function test_delete_cached_events_of_removed_event_sources() {
+		\add_filter( 'activitypub_defer_signature_verification', '__return_true' );
+
+		// Check that we have three event posts.
+		$event_query = Event_Query::get_instance();
+		$the_query   = $event_query->get_upcoming_events();
+		$this->assertEquals( 0, $the_query->post_count );
+
+		// Add second event source.
+		\Event_Bridge_For_ActivityPub\ActivityPub\Model\Event_Source::init_from_array( self::FOLLOWED_ACTOR_2 )->save();
+		\Event_Bridge_For_ActivityPub\ActivityPub\Collection\Event_Sources::delete_event_source_transients();
+
+		// Receive first event of first Organizer.
+		$json = array(
+			'id'     => 'https://remote.example/@organizer/events/new-year-party#create',
+			'type'   => 'Create',
+			'actor'  => 'https://remote.example/@organizer',
+			'object' => array(
+				'id'        => 'https://remote.example/@organizer/events/new-year-party',
+				'type'      => 'Event',
+				'name'      => 'Fediverse Party',
+				'startTime' => \gmdate( 'Y-m-d\TH:i:s\Z', time() + WEEK_IN_SECONDS ),
+				'endTime'   => \gmdate( 'Y-m-d\TH:i:s\Z', time() + WEEK_IN_SECONDS + HOUR_IN_SECONDS ),
+				'to'        => 'https://www.w3.org/ns/activitystreams#Public',
+				'published' => '2020-01-01T00:00:00Z',
+			),
+		);
+
+		$request  = new WP_REST_Request( 'POST', '/activitypub/1.0/users/0/inbox' );
+		$request->set_header( 'Content-Type', 'application/activity+json' );
+		$request->set_body( \wp_json_encode( $json ) );
+		$response = \rest_do_request( $request );
+		$this->assertEquals( 202, $response->get_status() );
+
+		$the_query   = $event_query->get_upcoming_events();
+		$this->assertEquals( 1, $the_query->post_count );
+
+		// Second event of first organizer.
+		$json = array(
+			'id'     => 'https://remote.example/@organizer/events/birthday-party#create',
+			'type'   => 'Create',
+			'actor'  => 'https://remote.example/@organizer',
+			'object' => array(
+				'id'        => 'https://remote.example/@organizer/events/birthday-party',
+				'type'      => 'Event',
+				'name'      => 'Fediverse Party',
+				'startTime' => \gmdate( 'Y-m-d\TH:i:s\Z', time() + 2* WEEK_IN_SECONDS ),
+				'endTime'   => \gmdate( 'Y-m-d\TH:i:s\Z', time() + 2* WEEK_IN_SECONDS + HOUR_IN_SECONDS ),
+				'to'        => 'https://www.w3.org/ns/activitystreams#Public',
+				'published' => '2020-01-01T00:00:00Z',
+			),
+		);
+		$request->set_body( \wp_json_encode( $json ) );
+		$response = \rest_do_request( $request );
+		$this->assertEquals( 202, $response->get_status() );
+		$the_query = $event_query->get_upcoming_events();
+		$this->assertEquals( 2, $the_query->post_count );
+
+		// Receive event of other organizer.
+		$json = array(
+			'id'     => 'https://remote.example/@organizer2/events/concert#create',
+			'type'   => 'Create',
+			'actor'  => 'https://remote.example/@organizer2',
+			'object' => array(
+				'id'        => 'https://remote.example/@organizer2/events/concert',
+				'type'      => 'Event',
+				'name'      => 'Concert',
+				'startTime' => \gmdate( 'Y-m-d\TH:i:s\Z', time() + 3 * WEEK_IN_SECONDS ),
+				'endTime'   => \gmdate( 'Y-m-d\TH:i:s\Z', time() + 3 * WEEK_IN_SECONDS + HOUR_IN_SECONDS ),
+				'to'        => 'https://www.w3.org/ns/activitystreams#Public',
+				'published' => '2020-01-01T00:00:00Z',
+			),
+		);
+		$request->set_body( \wp_json_encode( $json ) );
+		$response = \rest_do_request( $request );
+		$this->assertEquals( 202, $response->get_status() );
+		$the_query = $event_query->get_upcoming_events();
+		$this->assertEquals( 3, $the_query->post_count );
+
+		// Remove first event source.
+		$result = \Event_Bridge_For_ActivityPub\ActivityPub\Collection\Event_Sources::remove_event_source( 'https://remote.example/@organizer' );
+
+		// Verify that event posts got deleted.
+		$the_query   = $event_query->get_upcoming_events();
+		$this->assertEquals( 1, $the_query->post_count );
+
+		\remove_filter( 'activitypub_defer_signature_verification', '__return_true' );
+	}
 }