diff --git a/src/wp-admin/site-editor.php b/src/wp-admin/site-editor.php
index 71d289be7a02f..5a017dc722d6a 100644
--- a/src/wp-admin/site-editor.php
+++ b/src/wp-admin/site-editor.php
@@ -59,7 +59,10 @@ static function ( $classes ) {
 $context_settings = array( 'name' => 'core/edit-site' );
 
 if ( ! empty( $_GET['postId'] ) ) {
-	$context_settings['post'] = get_post( $_GET['postId'] );
+	$post_id = (int) $_GET['postId'];
+	if ( $post_id ) {
+		$context_settings['post'] = get_post( $post_id );
+	}
 }
 
 $block_editor_context = new WP_Block_Editor_Context( $context_settings );