diff --git a/syncapi/streams/stream_pdu.go b/syncapi/streams/stream_pdu.go
index 086e315c2..0d2378f14 100644
--- a/syncapi/streams/stream_pdu.go
+++ b/syncapi/streams/stream_pdu.go
@@ -3,19 +3,49 @@ package streams
 import (
 	"context"
 	"sync"
+	"time"
 
 	"github.com/matrix-org/dendrite/syncapi/types"
 	userapi "github.com/matrix-org/dendrite/userapi/api"
 	"github.com/matrix-org/gomatrixserverlib"
+	"go.uber.org/atomic"
 )
 
+const COMPLETE_SYNC_QUEUE = 2048
+const COMPLETE_SYNC_WORKERS = 256
+
 type PDUStreamProvider struct {
 	StreamProvider
+
+	tasks   chan func()
+	workers atomic.Int32
+}
+
+func (p *PDUStreamProvider) worker() {
+	defer p.workers.Dec()
+	for {
+		select {
+		case f := <-p.tasks:
+			f()
+		case <-time.After(time.Second * 10):
+			return
+		}
+	}
+}
+
+func (p *PDUStreamProvider) queue(f func()) {
+	p.tasks <- f
+	if p.workers.Load() < COMPLETE_SYNC_WORKERS {
+		p.workers.Inc()
+		go p.worker()
+	}
 }
 
 func (p *PDUStreamProvider) Setup() {
 	p.StreamProvider.Setup()
 
+	p.tasks = make(chan func(), COMPLETE_SYNC_QUEUE)
+
 	p.latestMutex.Lock()
 	defer p.latestMutex.Unlock()
 
@@ -56,24 +86,29 @@ func (p *PDUStreamProvider) CompleteSync(
 	var reqMutex sync.Mutex
 	var reqWaitGroup sync.WaitGroup
 	reqWaitGroup.Add(len(joinedRoomIDs))
-	for _, roomID := range joinedRoomIDs {
-		go func(roomID string) {
+	for _, room := range joinedRoomIDs {
+		roomID := room
+		p.queue(func() {
 			defer reqWaitGroup.Done()
+
 			var jr *types.JoinResponse
 			jr, err = p.getJoinResponseForCompleteSync(
 				ctx, roomID, r, &stateFilter, &eventFilter, req.Device,
 			)
 			if err != nil {
 				req.Log.WithError(err).Error("p.getJoinResponseForCompleteSync failed")
-				return //from
+				return
 			}
+
 			reqMutex.Lock()
 			defer reqMutex.Unlock()
 			req.Response.Rooms.Join[roomID] = *jr
 			req.Rooms[roomID] = gomatrixserverlib.Join
-		}(roomID)
+		})
 	}
 
+	reqWaitGroup.Wait()
+
 	// Add peeked rooms.
 	peeks, err := p.DB.PeeksInRange(ctx, req.Device.UserID, req.Device.ID, r)
 	if err != nil {