diff --git a/services/track-changes/app/coffee/MongoManager.coffee b/services/track-changes/app/coffee/MongoManager.coffee
index 71f926a745..330a903a8a 100644
--- a/services/track-changes/app/coffee/MongoManager.coffee
+++ b/services/track-changes/app/coffee/MongoManager.coffee
@@ -75,7 +75,21 @@ module.exports = MongoManager =
 
 		cursor.toArray callback
 
-	ensureIndices: (callback = (error) ->) ->
-		db.docHistory.ensureIndex { doc_id: 1, v: 1 }, callback
-		db.docHistory.ensureIndex { project_id: 1, "meta.end_ts": 1 }, callback
+	backportProjectId: (project_id, doc_id, callback = (error) ->) ->
+		db.docHistory.update {
+			doc_id: ObjectId(doc_id.toString())
+			project_id: { $exists: false }
+		}, {
+			$set: { project_id: ObjectId(project_id.toString()) }
+		}, {
+			multi: true
+		}, callback
+
+	ensureIndices: (callback = (error) ->) ->
+		# For finding all updates that go into a diff for a doc
+		db.docHistory.ensureIndex { doc_id: 1, v: 1 }, callback
+		# For finding all updates that affect a project
+		db.docHistory.ensureIndex { project_id: 1, "meta.end_ts": 1 }, callback
+		# For finding updates that don't yet have a project_id and need it inserting
+		db.docHistory.ensureIndex { doc_id: 1, project_id: 1 }, callback
 
diff --git a/services/track-changes/app/coffee/UpdatesManager.coffee b/services/track-changes/app/coffee/UpdatesManager.coffee
index 42cd38fad4..c13b42d326 100644
--- a/services/track-changes/app/coffee/UpdatesManager.coffee
+++ b/services/track-changes/app/coffee/UpdatesManager.coffee
@@ -38,23 +38,25 @@ module.exports = UpdatesManager =
 
 	REDIS_READ_BATCH_SIZE: 100
 	processUncompressedUpdates: (project_id, doc_id, callback = (error) ->) ->
-		RedisManager.getOldestRawUpdates doc_id, UpdatesManager.REDIS_READ_BATCH_SIZE, (error, rawUpdates) ->
+		MongoManager.backportProjectId project_id, doc_id, (error) ->
 			return callback(error) if error?
-			length = rawUpdates.length
-			UpdatesManager.compressAndSaveRawUpdates project_id, doc_id, rawUpdates, (error) ->
+			RedisManager.getOldestRawUpdates doc_id, UpdatesManager.REDIS_READ_BATCH_SIZE, (error, rawUpdates) ->
 				return callback(error) if error?
-				logger.log project_id: project_id, doc_id: doc_id, "compressed and saved doc updates"
-				RedisManager.deleteOldestRawUpdates project_id, doc_id, length, (error) ->
+				length = rawUpdates.length
+				UpdatesManager.compressAndSaveRawUpdates project_id, doc_id, rawUpdates, (error) ->
 					return callback(error) if error?
-					if length == UpdatesManager.REDIS_READ_BATCH_SIZE
-						# There might be more updates
-						logger.log project_id: project_id, doc_id: doc_id, "continuing processing updates"
-						setTimeout () ->
-							UpdatesManager.processUncompressedUpdates project_id, doc_id, callback
-						, 0
-					else
-						logger.log project_id: project_id, doc_id: doc_id, "all raw updates processed"
-						callback()
+					logger.log project_id: project_id, doc_id: doc_id, "compressed and saved doc updates"
+					RedisManager.deleteOldestRawUpdates project_id, doc_id, length, (error) ->
+						return callback(error) if error?
+						if length == UpdatesManager.REDIS_READ_BATCH_SIZE
+							# There might be more updates
+							logger.log project_id: project_id, doc_id: doc_id, "continuing processing updates"
+							setTimeout () ->
+								UpdatesManager.processUncompressedUpdates project_id, doc_id, callback
+							, 0
+						else
+							logger.log project_id: project_id, doc_id: doc_id, "all raw updates processed"
+							callback()
 
 	processUncompressedUpdatesWithLock: (project_id, doc_id, callback = (error) ->) ->
 		LockManager.runWithLock(
diff --git a/services/track-changes/test/unit/coffee/MongoManager/MongoManagerTests.coffee b/services/track-changes/test/unit/coffee/MongoManager/MongoManagerTests.coffee
index c5609994a1..b3a8fc04ca 100644
--- a/services/track-changes/test/unit/coffee/MongoManager/MongoManagerTests.coffee
+++ b/services/track-changes/test/unit/coffee/MongoManager/MongoManagerTests.coffee
@@ -252,3 +252,25 @@ describe "MongoManager", ->
 				@db.docHistory.limit
 					.calledWith(@limit)
 					.should.equal true
+
+	describe "backportProjectId", ->
+		beforeEach ->
+			@db.docHistory =
+				update: sinon.stub().callsArg(3)
+			@MongoManager.backportProjectId @project_id, @doc_id, @callback
+
+		it "should insert the project_id into all entries for the doc_id which don't have it set", ->
+			@db.docHistory.update
+				.calledWith({
+					doc_id: ObjectId(@doc_id)
+					project_id: { $exists: false }
+				}, {
+					$set: { project_id: ObjectId(@project_id) }
+				}, {
+					multi: true
+				})
+				.should.equal true
+
+		it "should call the callback", ->
+			@callback.called.should.equal true
+
diff --git a/services/track-changes/test/unit/coffee/UpdatesManager/UpdatesManagerTests.coffee b/services/track-changes/test/unit/coffee/UpdatesManager/UpdatesManagerTests.coffee
index 9bdf5fd635..6ff9f64e11 100644
--- a/services/track-changes/test/unit/coffee/UpdatesManager/UpdatesManagerTests.coffee
+++ b/services/track-changes/test/unit/coffee/UpdatesManager/UpdatesManagerTests.coffee
@@ -120,14 +120,22 @@ describe "UpdatesManager", ->
 						.should.equal true
 
 	describe "processUncompressedUpdates", ->
+		beforeEach ->
+			@UpdatesManager.compressAndSaveRawUpdates = sinon.stub().callsArgWith(3)
+			@RedisManager.deleteOldestRawUpdates = sinon.stub().callsArg(3)
+			@MongoManager.backportProjectId = sinon.stub().callsArg(2)
+
 		describe "when there is fewer than one batch to send", ->
 			beforeEach ->
 				@updates = ["mock-update"]
 				@RedisManager.getOldestRawUpdates = sinon.stub().callsArgWith(2, null, @updates)
-				@UpdatesManager.compressAndSaveRawUpdates = sinon.stub().callsArgWith(3)
-				@RedisManager.deleteOldestRawUpdates = sinon.stub().callsArg(3)
 				@UpdatesManager.processUncompressedUpdates @project_id, @doc_id, @callback
 
+			it "should backport the project id", ->
+				@MongoManager.backportProjectId
+					.calledWith(@project_id, @doc_id)
+					.should.equal true
+
 			it "should get the oldest updates", ->
 				@RedisManager.getOldestRawUpdates
 					.calledWith(@doc_id, @UpdatesManager.REDIS_READ_BATCH_SIZE)
@@ -156,8 +164,6 @@ describe "UpdatesManager", ->
 					@redisArray = @redisArray.slice(batchSize)
 					callback null, updates
 				sinon.spy @RedisManager, "getOldestRawUpdates"
-				@UpdatesManager.compressAndSaveRawUpdates = sinon.stub().callsArgWith(3)
-				@RedisManager.deleteOldestRawUpdates = sinon.stub().callsArg(3)
 				@UpdatesManager.processUncompressedUpdates @project_id, @doc_id, (args...) =>
 					@callback(args...)
 					done()