diff --git a/src/github.com/matrix-org/dendrite/federationapi/routing/backfill.go b/src/github.com/matrix-org/dendrite/federationapi/routing/backfill.go
index 1b5f138a0..d996db6a3 100644
--- a/src/github.com/matrix-org/dendrite/federationapi/routing/backfill.go
+++ b/src/github.com/matrix-org/dendrite/federationapi/routing/backfill.go
@@ -1,3 +1,5 @@
+// Copyright 2018 New Vector Ltd
+//
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
@@ -18,6 +20,8 @@ import (
 
 	"github.com/matrix-org/dendrite/clientapi/httputil"
 	"github.com/matrix-org/dendrite/clientapi/jsonerror"
+	"github.com/matrix-org/dendrite/common/config"
+	"github.com/matrix-org/dendrite/federationapi/types"
 	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
@@ -30,6 +34,7 @@ func Backfill(
 	request *gomatrixserverlib.FederationRequest,
 	query api.RoomserverQueryAPI,
 	roomID string,
+	cfg config.Dendrite,
 ) util.JSONResponse {
 	var res api.QueryBackfillResponse
 	var eIDs []string
@@ -84,11 +89,14 @@ func Backfill(
 			evs = append(evs, ev)
 		}
 	}
-	res.Events = evs
+
+	txn := types.NewTransaction()
+	txn.Origin = cfg.Matrix.ServerName
+	txn.PDUs = evs
 
 	// Send the events to the client.
 	return util.JSONResponse{
 		Code: http.StatusOK,
-		JSON: res,
+		JSON: txn,
 	}
 }
diff --git a/src/github.com/matrix-org/dendrite/federationapi/routing/routing.go b/src/github.com/matrix-org/dendrite/federationapi/routing/routing.go
index 24812f220..1ca4f6679 100644
--- a/src/github.com/matrix-org/dendrite/federationapi/routing/routing.go
+++ b/src/github.com/matrix-org/dendrite/federationapi/routing/routing.go
@@ -224,7 +224,7 @@ func Setup(
 		"federation_backfill", cfg.Matrix.ServerName, keys,
 		func(httpReq *http.Request, request *gomatrixserverlib.FederationRequest) util.JSONResponse {
 			vars := mux.Vars(httpReq)
-			return Backfill(httpReq, request, query, vars["roomID"])
+			return Backfill(httpReq, request, query, vars["roomID"], cfg)
 		},
 	)).Methods(http.MethodGet)
 }
diff --git a/src/github.com/matrix-org/dendrite/federationapi/types/types.go b/src/github.com/matrix-org/dendrite/federationapi/types/types.go
new file mode 100644
index 000000000..24838d547
--- /dev/null
+++ b/src/github.com/matrix-org/dendrite/federationapi/types/types.go
@@ -0,0 +1,43 @@
+// Copyright 2018 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package types
+
+import (
+	"time"
+
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+// Transaction is the representation of a transaction from the federation API
+// See https://matrix.org/docs/spec/server_server/unstable.html for more info.
+type Transaction struct {
+	// The server_name of the homeserver sending this transaction.
+	Origin gomatrixserverlib.ServerName `json:"origin"`
+	// POSIX timestamp in milliseconds on originating homeserver when this
+	// transaction started.
+	OriginServerTS int64 `json:"origin_server_ts"`
+	// List of persistent updates to rooms.
+	PDUs []gomatrixserverlib.Event `json:"pdus"`
+}
+
+// NewTransaction sets the timestamp of a new transaction instance and then
+// returns the said instance.
+func NewTransaction() Transaction {
+	// Retrieve the current timestamp in nanoseconds and make it a milliseconds
+	// one.
+	ts := time.Now().UnixNano() / int64(time.Millisecond)
+
+	return Transaction{OriginServerTS: ts}
+}