diff --git a/services/real-time/app/coffee/DocumentUpdaterController.coffee b/services/real-time/app/coffee/DocumentUpdaterController.coffee
index dcdd8d142c..a2bd3f3e77 100644
--- a/services/real-time/app/coffee/DocumentUpdaterController.coffee
+++ b/services/real-time/app/coffee/DocumentUpdaterController.coffee
@@ -4,6 +4,7 @@ redis = require("redis-sharelatex")
 rclient = redis.createClient(settings.redis.documentupdater)
 SafeJsonParse = require "./SafeJsonParse"
 EventLogger = require "./EventLogger"
+metrics = require "metrics-sharelatex"
 
 MESSAGE_SIZE_LOG_LIMIT = 1024 * 1024 # 1Mb
 
@@ -31,13 +32,20 @@ module.exports = DocumentUpdaterController =
 				logger.debug {message}, "got health check message in applied ops channel"
 
 	_applyUpdateFromDocumentUpdater: (io, doc_id, update) ->
-		for client in io.sockets.clients(doc_id)
+		clientList = io.sockets.clients(doc_id)
+		seen = {}
+		# send messages only to unique clients (due to duplicate entries in io.sockets.clients)
+		for client in clientList when not seen[client.id]
+			seen[client.id] = true
 			if client.id == update.meta.source
 				logger.log doc_id: doc_id, version: update.v, source: update.meta?.source, "distributing update to sender"
 				client.emit "otUpdateApplied", v: update.v, doc: update.doc
 			else if !update.dup # Duplicate ops should just be sent back to sending client for acknowledgement
 				logger.log doc_id: doc_id, version: update.v, source: update.meta?.source, client_id: client.id, "distributing update to collaborator"
 				client.emit "otUpdateApplied", update
+		if Object.keys(seen).length < clientList.length
+			metrics.inc "socket-io.duplicate-clients", 0.1
+			logger.log doc_id: doc_id, socketIoClients: (client.id for client in clientList), "discarded duplicate clients"
 
 	_processErrorFromDocumentUpdater: (io, doc_id, error, message) ->
 		for client in io.sockets.clients(doc_id)
@@ -46,5 +54,3 @@ module.exports = DocumentUpdaterController =
 			client.disconnect()
 
 
-
-
diff --git a/services/real-time/app/coffee/WebsocketLoadBalancer.coffee b/services/real-time/app/coffee/WebsocketLoadBalancer.coffee
index eeedb25916..4095e36e68 100644
--- a/services/real-time/app/coffee/WebsocketLoadBalancer.coffee
+++ b/services/real-time/app/coffee/WebsocketLoadBalancer.coffee
@@ -39,7 +39,12 @@ module.exports = WebsocketLoadBalancer =
 			else if message.room_id?
 				if message._id?
 					EventLogger.checkEventOrder("editor-events", message._id, message)
-				io.sockets.in(message.room_id).emit(message.message, message.payload...)
+				# send messages only to unique clients (due to duplicate entries in io.sockets.clients)
+				clientList = io.sockets.clients(message.room_id)
+				seen = {}
+				for client in clientList when not seen[client.id]
+					seen[client.id] = true
+					client.emit(message.message, message.payload...)
 			else if message.health_check?
 				logger.debug {message}, "got health check message in editor events channel"
 		
diff --git a/services/real-time/test/unit/coffee/DocumentUpdaterControllerTests.coffee b/services/real-time/test/unit/coffee/DocumentUpdaterControllerTests.coffee
index a2aee89cc0..c104646696 100644
--- a/services/real-time/test/unit/coffee/DocumentUpdaterControllerTests.coffee
+++ b/services/real-time/test/unit/coffee/DocumentUpdaterControllerTests.coffee
@@ -23,6 +23,7 @@ describe "DocumentUpdaterController", ->
 			"./SafeJsonParse": @SafeJsonParse =
 				parse: (data, cb) => cb null, JSON.parse(data)
 			"./EventLogger": @EventLogger = {checkEventOrder: sinon.stub()}
+			"metrics-sharelatex": @metrics = {inc: sinon.stub()}
 
 	describe "listenForUpdatesFromDocumentUpdater", ->
 		beforeEach ->
@@ -81,7 +82,7 @@ describe "DocumentUpdaterController", ->
 				v: @version = 42
 				doc: @doc_id
 			@io.sockets =
-				clients: sinon.stub().returns([@sourceClient, @otherClients...])
+				clients: sinon.stub().returns([@sourceClient, @otherClients..., @sourceClient]) # include a duplicate client
 		
 		describe "normally", ->
 			beforeEach ->
@@ -91,6 +92,7 @@ describe "DocumentUpdaterController", ->
 				@sourceClient.emit
 					.calledWith("otUpdateApplied", v: @version, doc: @doc_id)
 					.should.equal true
+				@sourceClient.emit.calledOnce.should.equal true
 
 			it "should get the clients connected to the document", ->
 				@io.sockets.clients
diff --git a/services/real-time/test/unit/coffee/WebsocketLoadBalancerTests.coffee b/services/real-time/test/unit/coffee/WebsocketLoadBalancerTests.coffee
index ad0c70832c..38c317e9fe 100644
--- a/services/real-time/test/unit/coffee/WebsocketLoadBalancerTests.coffee
+++ b/services/real-time/test/unit/coffee/WebsocketLoadBalancerTests.coffee
@@ -73,18 +73,24 @@ describe "WebsocketLoadBalancer", ->
 		describe "with a designated room", ->
 			beforeEach ->
 				@io.sockets =
-					in: sinon.stub().returns(emit: @emit = sinon.stub())
+					clients: sinon.stub().returns([
+						{id: 'client-id-1', emit: @emit1 = sinon.stub()}
+						{id: 'client-id-2', emit: @emit2 = sinon.stub()}
+						{id: 'client-id-1', emit: @emit3 = sinon.stub()} # duplicate client
+					])
 				data = JSON.stringify
 					room_id: @room_id
 					message: @message
 					payload: @payload
 				@WebsocketLoadBalancer._processEditorEvent(@io, "editor-events", data)
 
-			it "should send the message to all clients in the room", ->
-				@io.sockets.in
+			it "should send the message to all (unique) clients in the room", ->
+				@io.sockets.clients
 					.calledWith(@room_id)
 					.should.equal true
-				@emit.calledWith(@message, @payload...).should.equal true
+				@emit1.calledWith(@message, @payload...).should.equal true
+				@emit2.calledWith(@message, @payload...).should.equal true
+				@emit3.called.should.equal false # duplicate client should be ignored
 
 		describe "when emitting to all", ->
 			beforeEach ->