diff --git a/federationapi/routing/backfill.go b/federationapi/routing/backfill.go
index 1f46b240f..0d3893de3 100644
--- a/federationapi/routing/backfill.go
+++ b/federationapi/routing/backfill.go
@@ -102,7 +102,7 @@ func Backfill(
 		}
 	}
 
-	var eventJSONs []json.RawMessage
+	eventJSONs := []json.RawMessage{}
 	for _, e := range gomatrixserverlib.ReverseTopologicalOrdering(
 		evs,
 		gomatrixserverlib.TopologicalOrderByPrevEvents,
diff --git a/syncapi/sync/request.go b/syncapi/sync/request.go
index 66663cf0a..c7796b561 100644
--- a/syncapi/sync/request.go
+++ b/syncapi/sync/request.go
@@ -16,6 +16,7 @@ package sync
 
 import (
 	"context"
+	"encoding/json"
 	"net/http"
 	"strconv"
 	"time"
@@ -30,6 +31,14 @@ import (
 const defaultSyncTimeout = time.Duration(0)
 const defaultTimelineLimit = 20
 
+type filter struct {
+	Room struct {
+		Timeline struct {
+			Limit *int `json:"limit"`
+		} `json:"timeline"`
+	} `json:"room"`
+}
+
 // syncRequest represents a /sync request, with sensible defaults/sanity checks applied.
 type syncRequest struct {
 	ctx           context.Context
@@ -54,6 +63,17 @@ func newSyncRequest(req *http.Request, device authtypes.Device) (*syncRequest, e
 		}
 		since = &tok
 	}
+	timelineLimit := defaultTimelineLimit
+	// TODO: read from stored filters too
+	filterQuery := req.URL.Query().Get("filter")
+	if filterQuery != "" && filterQuery[0] == '{' {
+		// attempt to parse the timeline limit at least
+		var f filter
+		err := json.Unmarshal([]byte(filterQuery), &f)
+		if err == nil && f.Room.Timeline.Limit != nil {
+			timelineLimit = *f.Room.Timeline.Limit
+		}
+	}
 	// TODO: Additional query params: set_presence, filter
 	return &syncRequest{
 		ctx:           req.Context(),
@@ -61,7 +81,7 @@ func newSyncRequest(req *http.Request, device authtypes.Device) (*syncRequest, e
 		timeout:       timeout,
 		since:         since,
 		wantFullState: wantFullState,
-		limit:         defaultTimelineLimit, // TODO: read from filter
+		limit:         timelineLimit,
 		log:           util.GetLogger(req.Context()),
 	}, nil
 }
diff --git a/syncapi/sync/requestpool.go b/syncapi/sync/requestpool.go
index 6e0f44e9a..82ce283b6 100644
--- a/syncapi/sync/requestpool.go
+++ b/syncapi/sync/requestpool.go
@@ -59,6 +59,7 @@ func (rp *RequestPool) OnIncomingSyncRequest(req *http.Request, device *authtype
 		"userID":  userID,
 		"since":   syncReq.since,
 		"timeout": syncReq.timeout,
+		"limit":   syncReq.limit,
 	})
 
 	currPos := rp.notifier.CurrentPosition()
diff --git a/sytest-whitelist b/sytest-whitelist
index 2e8205dcd..d5b4feaf6 100644
--- a/sytest-whitelist
+++ b/sytest-whitelist
@@ -281,3 +281,5 @@ An event which redacts itself should be ignored
 A pair of events which redact each other should be ignored
 Outbound federation can backfill events
 Inbound federation can backfill events
+Backfill checks the events requested belong to the room
+Backfilled events whose prev_events are in a different room do not allow cross-room back-pagination