diff --git a/includes/class-newspack-popups-model.php b/includes/class-newspack-popups-model.php
index baf051a7..decc9482 100644
--- a/includes/class-newspack-popups-model.php
+++ b/includes/class-newspack-popups-model.php
@@ -257,6 +257,7 @@ public static function get_preview_query_options() {
 			'archive_insertion_posts_count'  => FILTER_SANITIZE_FULL_SPECIAL_CHARS,
 			'archive_insertion_is_repeating' => FILTER_VALIDATE_BOOLEAN,
 			'utm_suppression'                => FILTER_SANITIZE_FULL_SPECIAL_CHARS,
+			'additional_classes'             => FILTER_SANITIZE_FULL_SPECIAL_CHARS,
 		];
 
 		$options = [];
diff --git a/includes/class-newspack-popups.php b/includes/class-newspack-popups.php
index 522e20f4..8950e7b9 100644
--- a/includes/class-newspack-popups.php
+++ b/includes/class-newspack-popups.php
@@ -40,6 +40,7 @@ final class Newspack_Popups {
 		'archive_insertion_posts_count'  => 'n_ac',
 		'archive_insertion_is_repeating' => 'n_ar',
 		'utm_suppression'                => 'n_ut',
+		'additional_classes'             => 'n_acl',
 	];
 
 	/**