diff --git a/syncapi/syncapi_test.go b/syncapi/syncapi_test.go
index 089bdafaf..8b33c5e43 100644
--- a/syncapi/syncapi_test.go
+++ b/syncapi/syncapi_test.go
@@ -154,8 +154,12 @@ func testSyncAccessTokens(t *testing.T, dbType test.DBType) {
 			wantJoinedRooms: []string{room.ID},
 		},
 	}
-	// TODO: find a better way
-	time.Sleep(500 * time.Millisecond)
+
+	syncUntil(t, base, alice.AccessToken, false, func(syncBody string) bool {
+		// wait for the last sent eventID to come down sync
+		path := fmt.Sprintf(`rooms.join.%s.timeline.events.#(event_id=="%s")`, room.ID, room.Events()[len(room.Events())-1].EventID())
+		return gjson.Get(syncBody, path).Exists()
+	})
 
 	for _, tc := range testCases {
 		w := httptest.NewRecorder()
@@ -343,6 +347,13 @@ func testHistoryVisibility(t *testing.T, dbType test.DBType) {
 
 	// create the users
 	alice := test.NewUser(t)
+	aliceDev := userapi.Device{
+		ID:          "ALICEID",
+		UserID:      alice.ID,
+		AccessToken: "ALICE_BEARER_TOKEN",
+		DisplayName: "ALICE",
+	}
+
 	bob := test.NewUser(t)
 
 	bobDev := userapi.Device{
@@ -409,7 +420,7 @@ func testHistoryVisibility(t *testing.T, dbType test.DBType) {
 		rsAPI := roomserver.NewInternalAPI(base)
 		rsAPI.SetFederationAPI(nil, nil)
 
-		AddPublicRoutes(base, &syncUserAPI{accounts: []userapi.Device{bobDev}}, rsAPI, &syncKeyAPI{})
+		AddPublicRoutes(base, &syncUserAPI{accounts: []userapi.Device{aliceDev, bobDev}}, rsAPI, &syncKeyAPI{})
 
 		for _, tc := range testCases {
 			testname := fmt.Sprintf("%s - %s", tc.historyVisibility, userType)
@@ -418,12 +429,18 @@ func testHistoryVisibility(t *testing.T, dbType test.DBType) {
 				room := test.NewRoom(t, alice, test.RoomHistoryVisibility(tc.historyVisibility))
 
 				// send the events/messages to NATS to create the rooms
-				beforeJoinEv := room.CreateAndInsert(t, alice, "m.room.message", map[string]interface{}{"body": fmt.Sprintf("Before invite in a %s room", tc.historyVisibility)})
+				beforeJoinBody := fmt.Sprintf("Before invite in a %s room", tc.historyVisibility)
+				beforeJoinEv := room.CreateAndInsert(t, alice, "m.room.message", map[string]interface{}{"body": beforeJoinBody})
 				eventsToSend := append(room.Events(), beforeJoinEv)
 				if err := api.SendEvents(ctx, rsAPI, api.KindNew, eventsToSend, "test", "test", nil, false); err != nil {
 					t.Fatalf("failed to send events: %v", err)
 				}
-				time.Sleep(100 * time.Millisecond) // TODO: find a better way
+				syncUntil(t, base, aliceDev.AccessToken, false,
+					func(syncBody string) bool {
+						path := fmt.Sprintf(`rooms.join.%s.timeline.events.#(content.body=="%s")`, room.ID, beforeJoinBody)
+						return gjson.Get(syncBody, path).Exists()
+					},
+				)
 
 				// There is only one event, we expect only to be able to see this, if the room is world_readable
 				w := httptest.NewRecorder()
@@ -449,14 +466,20 @@ func testHistoryVisibility(t *testing.T, dbType test.DBType) {
 				inviteEv := room.CreateAndInsert(t, alice, "m.room.member", map[string]interface{}{"membership": "invite"}, test.WithStateKey(bob.ID))
 				afterInviteEv := room.CreateAndInsert(t, alice, "m.room.message", map[string]interface{}{"body": fmt.Sprintf("After invite in a %s room", tc.historyVisibility)})
 				joinEv := room.CreateAndInsert(t, bob, "m.room.member", map[string]interface{}{"membership": "join"}, test.WithStateKey(bob.ID))
-				msgEv := room.CreateAndInsert(t, alice, "m.room.message", map[string]interface{}{"body": fmt.Sprintf("After join in a %s room", tc.historyVisibility)})
+				afterJoinBody := fmt.Sprintf("After join in a %s room", tc.historyVisibility)
+				msgEv := room.CreateAndInsert(t, alice, "m.room.message", map[string]interface{}{"body": afterJoinBody})
 
 				eventsToSend = append([]*gomatrixserverlib.HeaderedEvent{}, inviteEv, afterInviteEv, joinEv, msgEv)
 
 				if err := api.SendEvents(ctx, rsAPI, api.KindNew, eventsToSend, "test", "test", nil, false); err != nil {
 					t.Fatalf("failed to send events: %v", err)
 				}
-				time.Sleep(100 * time.Millisecond) // TODO: find a better way
+				syncUntil(t, base, aliceDev.AccessToken, false,
+					func(syncBody string) bool {
+						path := fmt.Sprintf(`rooms.join.%s.timeline.events.#(content.body=="%s")`, room.ID, afterJoinBody)
+						return gjson.Get(syncBody, path).Exists()
+					},
+				)
 
 				// Verify the messages after/before invite are visible or not
 				w = httptest.NewRecorder()
@@ -511,8 +534,8 @@ func testSendToDevice(t *testing.T, dbType test.DBType) {
 		AccountType: userapi.AccountTypeUser,
 	}
 
-	base, close := testrig.CreateBaseDendrite(t, dbType)
-	defer close()
+	base, baseClose := testrig.CreateBaseDendrite(t, dbType)
+	defer baseClose()
 
 	jsctx, _ := base.NATS.Prepare(base.ProcessContext, &base.Cfg.Global.JetStream)
 	defer jetstream.DeleteAllStreams(jsctx, &base.Cfg.Global.JetStream)
@@ -607,7 +630,14 @@ func testSendToDevice(t *testing.T, dbType test.DBType) {
 				t.Fatalf("unable to send to device message: %v", err)
 			}
 		}
-		time.Sleep((time.Millisecond * 15) * time.Duration(tc.sendMessagesCount)) // wait a bit, so the messages can be processed
+
+		syncUntil(t, base, alice.AccessToken,
+			len(tc.want) == 0,
+			func(body string) bool {
+				return gjson.Get(body, fmt.Sprintf(`to_device.events.#(content.dummy=="message %d")`, msgCounter)).Exists()
+			},
+		)
+
 		// Execute a /sync request, recording the response
 		w := httptest.NewRecorder()
 		base.PublicClientAPIMux.ServeHTTP(w, test.NewRequest(t, "GET", "/_matrix/client/v3/sync", test.WithQueryParams(map[string]string{
@@ -630,6 +660,42 @@ func testSendToDevice(t *testing.T, dbType test.DBType) {
 	}
 }
 
+func syncUntil(t *testing.T,
+	base *base.BaseDendrite, accessToken string,
+	skip bool,
+	checkFunc func(syncBody string) bool,
+) {
+	if checkFunc == nil {
+		t.Fatalf("No checkFunc defined")
+	}
+	if skip {
+		return
+	}
+	// loop on /sync until we receive the last send message or timeout after 5 seconds, since we don't know if the message made it
+	// to the syncAPI when hitting /sync
+	done := make(chan bool)
+	defer close(done)
+	go func() {
+		for {
+			w := httptest.NewRecorder()
+			base.PublicClientAPIMux.ServeHTTP(w, test.NewRequest(t, "GET", "/_matrix/client/v3/sync", test.WithQueryParams(map[string]string{
+				"access_token": accessToken,
+				"timeout":      "1000",
+			})))
+			if checkFunc(w.Body.String()) {
+				done <- true
+				return
+			}
+		}
+	}()
+
+	select {
+	case <-done:
+	case <-time.After(time.Second * 5):
+		t.Fatalf("Timed out waiting for messages")
+	}
+}
+
 func toNATSMsgs(t *testing.T, base *base.BaseDendrite, input ...*gomatrixserverlib.HeaderedEvent) []*nats.Msg {
 	result := make([]*nats.Msg, len(input))
 	for i, ev := range input {