diff --git a/src/upgrades/1.1.0/dismiss_flags_from_deleted_topics.js b/src/upgrades/1.1.0/dismiss_flags_from_deleted_topics.js
index 6cbf6b7254..37e2fce239 100644
--- a/src/upgrades/1.1.0/dismiss_flags_from_deleted_topics.js
+++ b/src/upgrades/1.1.0/dismiss_flags_from_deleted_topics.js
@@ -34,8 +34,72 @@ module.exports = {
 				}).filter(Boolean);
 
 				winston.verbose('[2016/04/29] ' + toDismiss.length + ' dismissable flags found');
-				async.each(toDismiss, posts.dismissFlag, next);
+				async.each(toDismiss, dismissFlag, next);
 			},
 		], callback);
 	},
 };
+
+// copied from core since this function was removed
+// https://github.com/NodeBB/NodeBB/blob/v1.x.x/src/posts/flags.js
+function dismissFlag(pid, callback) {
+	async.waterfall([
+		function (next) {
+			db.getObjectFields('post:' + pid, ['pid', 'uid', 'flags'], next);
+		},
+		function (postData, next) {
+			if (!postData.pid) {
+				return callback();
+			}
+			async.parallel([
+				function (next) {
+					if (parseInt(postData.uid, 10)) {
+						if (parseInt(postData.flags, 10) > 0) {
+							async.parallel([
+								async.apply(db.sortedSetIncrBy, 'users:flags', -postData.flags, postData.uid),
+								async.apply(db.incrObjectFieldBy, 'user:' + postData.uid, 'flags', -postData.flags),
+							], next);
+						} else {
+							next();
+						}
+					} else {
+						next();
+					}
+				},
+				function (next) {
+					db.sortedSetsRemove([
+						'posts:flagged',
+						'posts:flags:count',
+						'uid:' + postData.uid + ':flag:pids',
+					], pid, next);
+				},
+				function (next) {
+					async.series([
+						function (next) {
+							db.getSortedSetRange('pid:' + pid + ':flag:uids', 0, -1, function (err, uids) {
+								if (err) {
+									return next(err);
+								}
+
+								async.each(uids, function (uid, next) {
+									var nid = 'post_flag:' + pid + ':uid:' + uid;
+									async.parallel([
+										async.apply(db.delete, 'notifications:' + nid),
+										async.apply(db.sortedSetRemove, 'notifications', 'post_flag:' + pid + ':uid:' + uid),
+									], next);
+								}, next);
+							});
+						},
+						async.apply(db.delete, 'pid:' + pid + ':flag:uids'),
+					], next);
+				},
+				async.apply(db.deleteObjectField, 'post:' + pid, 'flags'),
+				async.apply(db.delete, 'pid:' + pid + ':flag:uid:reason'),
+				async.apply(db.deleteObjectFields, 'post:' + pid, ['flag:state', 'flag:assignee', 'flag:notes', 'flag:history']),
+			], next);
+		},
+		function (results, next) {
+			db.sortedSetsRemoveRangeByScore(['users:flags'], '-inf', 0, next);
+		},
+	], callback);
+}