diff --git a/src/socket.io/topics.js b/src/socket.io/topics.js
index f8d333e67a..a7aa7a3ab0 100644
--- a/src/socket.io/topics.js
+++ b/src/socket.io/topics.js
@@ -16,6 +16,7 @@ require('./topics/move')(SocketTopics);
 require('./topics/tools')(SocketTopics);
 require('./topics/infinitescroll')(SocketTopics);
 require('./topics/tags')(SocketTopics);
+require('./topics/merge')(SocketTopics);
 
 SocketTopics.post = function (socket, data, callback) {
 	if (!data) {
diff --git a/src/socket.io/topics/merge.js b/src/socket.io/topics/merge.js
new file mode 100644
index 0000000000..54275606e6
--- /dev/null
+++ b/src/socket.io/topics/merge.js
@@ -0,0 +1,27 @@
+'use strict';
+
+var async = require('async');
+var topics = require('../../topics');
+var privileges = require('../../privileges');
+
+module.exports = function (SocketTopics) {
+	SocketTopics.merge = function (socket, tids, callback) {
+		if (!Array.isArray(tids)) {
+			return callback(new Error('[[error:invalid-data]]'));
+		}
+
+		async.waterfall([
+			function (next) {
+				async.map(tids, function (tid, next) {
+					privileges.topics.isAdminOrMod(tid, socket.uid, next);
+				}, next);
+			},
+			function (allowed, next) {
+				if (allowed.includes(false)) {
+					return next(new Error('[[error:no-privileges]]'));
+				}
+				topics.merge(tids, next);
+			},
+		], callback);
+	};
+};
diff --git a/src/topics.js b/src/topics.js
index 5f744316c0..44c263210d 100644
--- a/src/topics.js
+++ b/src/topics.js
@@ -31,6 +31,7 @@ require('./topics/suggested')(Topics);
 require('./topics/tools')(Topics);
 require('./topics/thumb')(Topics);
 require('./topics/bookmarks')(Topics);
+require('./topics/merge')(Topics);
 
 Topics.exists = function (tid, callback) {
 	db.isSortedSetMember('topics:tid', tid, callback);
@@ -252,7 +253,7 @@ function getMainPostAndReplies(topic, set, uid, start, stop, reverse, callback)
 				return callback(null, []);
 			}
 
-			if (topic.mainPid && start === 0) {
+			if (parseInt(topic.mainPid, 10) && start === 0) {
 				pids.unshift(topic.mainPid);
 			}
 			posts.getPostsByPids(pids, uid, next);
diff --git a/src/topics/merge.js b/src/topics/merge.js
new file mode 100644
index 0000000000..2c1df0df61
--- /dev/null
+++ b/src/topics/merge.js
@@ -0,0 +1,33 @@
+'use strict';
+
+var async = require('async');
+
+module.exports = function (Topics) {
+	Topics.merge = function (tids, callback) {
+		var mergeIntoTid = findOldestTopic(tids);
+
+		var otherTids = tids.filter(function (tid) {
+			return tid && parseInt(tid, 10) !== parseInt(mergeIntoTid, 10);
+		});
+
+		async.eachSeries(otherTids, function (tid, next) {
+			async.waterfall([
+				function (next) {
+					Topics.getPids(tid, next);
+				},
+				function (pids, next) {
+					async.eachSeries(pids, function (pid, next) {
+						Topics.movePostToTopic(pid, mergeIntoTid, next);
+					}, next);
+				},
+				function (next) {
+					Topics.setTopicField(tid, 'mainPid', 0, next);
+				},
+			], next);
+		}, callback);
+	};
+
+	function findOldestTopic(tids) {
+		return Math.min.apply(null, tids);
+	}
+};
diff --git a/src/topics/posts.js b/src/topics/posts.js
index ebfbd106c0..9816d8178f 100644
--- a/src/topics/posts.js
+++ b/src/topics/posts.js
@@ -326,7 +326,7 @@ module.exports = function (Topics) {
 				}, next);
 			},
 			function (results, next) {
-				if (results.mainPid) {
+				if (parseInt(results.mainPid, 10)) {
 					results.pids = [results.mainPid].concat(results.pids);
 				}
 				next(null, results.pids);
diff --git a/test/topics.js b/test/topics.js
index e6c341cb9e..15b839f996 100644
--- a/test/topics.js
+++ b/test/topics.js
@@ -1699,4 +1699,89 @@ describe('Topic\'s', function () {
 			});
 		});
 	});
+
+	describe('topic merge', function (done) {
+		var uid;
+		var topic1Data;
+		var topic2Data;
+
+		before(function (done) {
+			async.waterfall([
+				function (next) {
+					User.create({ username: 'mergevictim' }, next);
+				},
+				function (_uid, next) {
+					uid = _uid;
+					topics.post({ uid: uid, cid: categoryObj.cid, title: 'topic 1', content: 'topic 1 OP' }, next);
+				},
+				function (result, next) {
+					topic1Data = result.topicData;
+					topics.post({ uid: uid, cid: categoryObj.cid, title: 'topic 2', content: 'topic 2 OP' }, next);
+				},
+				function (result, next) {
+					topic2Data = result.topicData;
+					topics.reply({ uid: uid, content: 'topic 1 reply', tid: topic1Data.tid }, next);
+				},
+				function (postData, next) {
+					topics.reply({ uid: uid, content: 'topic 2 reply', tid: topic2Data.tid }, next);
+				},
+			], done);
+		});
+
+		it('should error if data is not an array', function (done) {
+			socketTopics.merge({ uid: 0 }, null, function (err) {
+				assert.equal(err.message, '[[error:invalid-data]]');
+				done();
+			});
+		});
+
+		it('should error if user does not have privileges', function (done) {
+			socketTopics.merge({ uid: 0 }, [topic2Data.tid, topic1Data.tid], function (err) {
+				assert.equal(err.message, '[[error:no-privileges]]');
+				done();
+			});
+		});
+
+		it('should merge 2 topics', function (done) {
+			async.waterfall([
+				function (next) {
+					socketTopics.merge({ uid: adminUid }, [topic2Data.tid, topic1Data.tid], next);
+				},
+				function (next) {
+					async.parallel({
+						topic1: function (next) {
+							async.waterfall([
+								function (next) {
+									topics.getTopicData(topic1Data.tid, next);
+								},
+								function (topicData, next) {
+									topics.getTopicWithPosts(topicData, 'tid:' + topicData.tid + ':posts', adminUid, 0, 19, false, next);
+								},
+							], next);
+						},
+						topic2: function (next) {
+							async.waterfall([
+								function (next) {
+									topics.getTopicData(topic2Data.tid, next);
+								},
+								function (topicData, next) {
+									topics.getTopicWithPosts(topicData, 'tid:' + topicData.tid + ':posts', adminUid, 0, 19, false, next);
+								},
+							], next);
+						},
+					}, next);
+				},
+				function (results, next) {
+					assert.equal(results.topic1.posts.length, 4);
+					assert.equal(results.topic2.posts.length, 0);
+
+					assert.equal(results.topic1.posts[0].content, 'topic 1 OP');
+					assert.equal(results.topic1.posts[1].content, 'topic 2 OP');
+					assert.equal(results.topic1.posts[2].content, 'topic 1 reply');
+					assert.equal(results.topic1.posts[3].content, 'topic 2 reply');
+					done();
+				},
+			], done);
+		});
+	});
 });