diff --git a/modules/pref-prefs.php b/modules/pref-prefs.php
index 2dbd206a3..87f8b6424 100644
--- a/modules/pref-prefs.php
+++ b/modules/pref-prefs.php
@@ -15,7 +15,8 @@
 			"PURGE_UNREAD_ARTICLES", "DIGEST_ENABLE", "DIGEST_CATCHUP",
 			"BLACKLISTED_TAGS", "ENABLE_FEED_ICONS", "ENABLE_API_ACCESS",
 			"UPDATE_POST_ON_CHECKSUM_CHANGE", "DEFAULT_UPDATE_INTERVAL",
-			"MARK_UNREAD_ON_UPDATE", "USER_TIMEZONE", "SORT_HEADLINES_BY_FEED_DATE");
+			"MARK_UNREAD_ON_UPDATE", "USER_TIMEZONE", "SORT_HEADLINES_BY_FEED_DATE",
+			"SSL_CERT_SERIAL");
 
 		if (FORCE_ARTICLE_PURGE != 0) {
 			array_push($prefs_blacklist, "PURGE_OLD_DAYS");