diff --git a/services/real-time/app/coffee/WebsocketController.coffee b/services/real-time/app/coffee/WebsocketController.coffee
index d091c5e4ed..1e4ca5160c 100644
--- a/services/real-time/app/coffee/WebsocketController.coffee
+++ b/services/real-time/app/coffee/WebsocketController.coffee
@@ -1,5 +1,6 @@
 logger = require "logger-sharelatex"
 metrics = require "metrics-sharelatex"
+settings = require "settings-sharelatex"
 WebApiManager = require "./WebApiManager"
 AuthorizationManager = require "./AuthorizationManager"
 DocumentUpdaterManager = require "./DocumentUpdaterManager"
@@ -202,6 +203,23 @@ module.exports = WebsocketController =
 		Utils.getClientAttributes client, ["user_id", "project_id"], (error, {user_id, project_id}) ->
 			return callback(error) if error?
 			return callback(new Error("no project_id found on client")) if !project_id?
+
+			updateSize = JSON.stringify(update).length
+			if updateSize > settings.maxUpdateSize
+				metrics.inc "update_too_large"
+				logger.warn({user_id, project_id, doc_id, updateSize}, "update is too large")
+
+				# mark the update as received -- the client should not send it again!
+				callback()
+
+				# trigger an out-of-sync error
+				message = {project_id, doc_id, error: "update is too large"}
+				setTimeout () ->
+					client.emit "otUpdateError", message.error, message
+					client.disconnect()
+				, 100
+				return
+
 			WebsocketController._assertClientCanApplyUpdate client, doc_id, update, (error) ->
 				if error?
 					logger.warn {err: error, doc_id, client_id: client.id, version: update.v}, "client is not authorized to make update"
diff --git a/services/real-time/config/settings.defaults.coffee b/services/real-time/config/settings.defaults.coffee
index 5814530552..9ca2348b0b 100644
--- a/services/real-time/config/settings.defaults.coffee
+++ b/services/real-time/config/settings.defaults.coffee
@@ -52,6 +52,11 @@ settings =
 	
 	max_doc_length: 2 * 1024 * 1024 # 2mb
 
+	# combine
+	# max_doc_length (2mb see above) * 2 (delete + insert)
+	# max_ranges_size (3mb see MAX_RANGES_SIZE in doc-updater) 
+	maxUpdateSize: parseInt(process.env['MAX_UPDATE_SIZE']) or 7 * 1024 * 1024
+
 	shutdownDrainTimeWindow: process.env['SHUTDOWN_DRAIN_TIME_WINDOW'] or 9
 
 	continualPubsubTraffic: process.env['CONTINUAL_PUBSUB_TRAFFIC'] or false
diff --git a/services/real-time/test/acceptance/coffee/ApplyUpdateTests.coffee b/services/real-time/test/acceptance/coffee/ApplyUpdateTests.coffee
index 842e4fcc4c..2d52975d71 100644
--- a/services/real-time/test/acceptance/coffee/ApplyUpdateTests.coffee
+++ b/services/real-time/test/acceptance/coffee/ApplyUpdateTests.coffee
@@ -68,6 +68,60 @@ describe "applyOtUpdate", ->
 				(cb) => rclient.del redisSettings.documentupdater.key_schema.pendingUpdates(@doc_id), cb
 			], done
 		
+	describe "when authorized with a huge edit update", ->
+		before (done) ->
+			@update = {
+				op: {p: 12, t: "foo"},
+				junk: 'this update is too large'.repeat(1024 * 300) # >7MB
+			}
+			async.series [
+				(cb) =>
+					FixturesManager.setUpProject {
+						privilegeLevel: "readAndWrite"
+					}, (e, {@project_id, @user_id}) =>
+						cb(e)
+
+				(cb) =>
+					FixturesManager.setUpDoc @project_id, {@lines, @version, @ops}, (e, {@doc_id}) =>
+						cb(e)
+
+				(cb) =>
+					@client = RealTimeClient.connect()
+					@client.on "connectionAccepted", cb
+					@client.on "otUpdateError", (@otUpdateError) =>
+
+				(cb) =>
+					@client.emit "joinProject", project_id: @project_id, cb
+
+				(cb) =>
+					@client.emit "joinDoc", @doc_id, cb
+
+				(cb) =>
+					@client.emit "applyOtUpdate", @doc_id, @update, (@error) =>
+						cb()
+			], done
+
+		it "should not return an error", ->
+			expect(@error).to.not.exist
+
+		it "should send an otUpdateError to the client", (done) ->
+			setTimeout () =>
+				expect(@otUpdateError).to.exist
+				done()
+			, 300
+
+		it "should disconnect the client", (done) ->
+			setTimeout () =>
+				@client.socket.connected.should.equal false
+				done()
+			, 300
+
+		it "should not put the update in redis", (done) ->
+			rclient.llen redisSettings.documentupdater.key_schema.pendingUpdates({@doc_id}), (error, len) =>
+				len.should.equal 0
+				done()
+			return null
+
 	describe "when authorized to read-only with an edit update", ->
 		before (done) ->
 			async.series [
diff --git a/services/real-time/test/unit/coffee/WebsocketControllerTests.coffee b/services/real-time/test/unit/coffee/WebsocketControllerTests.coffee
index f2f1531834..b6b4520ced 100644
--- a/services/real-time/test/unit/coffee/WebsocketControllerTests.coffee
+++ b/services/real-time/test/unit/coffee/WebsocketControllerTests.coffee
@@ -32,6 +32,7 @@ describe 'WebsocketController', ->
 			"./DocumentUpdaterManager": @DocumentUpdaterManager = {}
 			"./ConnectedUsersManager": @ConnectedUsersManager = {}
 			"./WebsocketLoadBalancer": @WebsocketLoadBalancer = {}
+			"settings-sharelatex": {maxUpdateSize: 7 * 1024 * 1024}
 			"logger-sharelatex": @logger = { log: sinon.stub(), error: sinon.stub(), warn: sinon.stub() }
 			"metrics-sharelatex": @metrics =
 				inc: sinon.stub()
@@ -668,6 +669,37 @@ describe 'WebsocketController', ->
 			it "should call the callback with the error", ->
 				@callback.calledWith(@error).should.equal true
 
+		describe "update_too_large", ->
+			beforeEach (done) ->
+				@client.disconnect = sinon.stub()
+				@client.emit = sinon.stub()
+				@update = {
+					op: {p: 12, t: "foo"},
+					junk: 'this update is too large'.repeat(1024 * 300) # >7MB
+				}
+				@client.params.user_id = @user_id
+				@client.params.project_id = @project_id
+				@WebsocketController.applyOtUpdate @client, @doc_id, @update, @callback
+				setTimeout ->
+					done()
+				, 201
+
+			it "should call the callback with no error", ->
+				@callback.called.should.equal true
+				@callback.args[0].should.deep.equal []
+
+			it "should log a warning with the size and context", ->
+				@logger.warn.called.should.equal true
+				@logger.warn.args[0].should.deep.equal [{
+					@user_id, @project_id, @doc_id, updateSize: 7372835
+				}, 'update is too large']
+
+			it "should send an otUpdateError the client", ->
+				@client.emit.calledWith('otUpdateError').should.equal true
+
+			it "should disconnect the client", ->
+				@client.disconnect.called.should.equal true
+
 	describe "_assertClientCanApplyUpdate", ->
 		beforeEach ->
 			@edit_update = { op: [{i: "foo", p: 42}, {c: "bar", p: 132}] } # comments may still be in an edit op