diff --git a/federationapi/routing/routing.go b/federationapi/routing/routing.go
index 9808d623..30a65271 100644
--- a/federationapi/routing/routing.go
+++ b/federationapi/routing/routing.go
@@ -82,7 +82,7 @@ func Setup(
 		func(httpReq *http.Request, request *gomatrixserverlib.FederationRequest, vars map[string]string) util.JSONResponse {
 			return Send(
 				httpReq, request, gomatrixserverlib.TransactionID(vars["txnID"]),
-				cfg, rsAPI, eduAPI, keys, federation,
+				cfg, rsAPI, eduAPI, keyAPI, keys, federation,
 			)
 		},
 	)).Methods(http.MethodPut, http.MethodOptions)
diff --git a/federationapi/routing/send.go b/federationapi/routing/send.go
index 680eaccd..903a2f22 100644
--- a/federationapi/routing/send.go
+++ b/federationapi/routing/send.go
@@ -23,6 +23,7 @@ import (
 	"github.com/matrix-org/dendrite/clientapi/jsonerror"
 	eduserverAPI "github.com/matrix-org/dendrite/eduserver/api"
 	"github.com/matrix-org/dendrite/internal/config"
+	keyapi "github.com/matrix-org/dendrite/keyserver/api"
 	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
@@ -37,6 +38,7 @@ func Send(
 	cfg *config.Dendrite,
 	rsAPI api.RoomserverInternalAPI,
 	eduAPI eduserverAPI.EDUServerInputAPI,
+	keyAPI keyapi.KeyInternalAPI,
 	keys gomatrixserverlib.JSONVerifier,
 	federation *gomatrixserverlib.FederationClient,
 ) util.JSONResponse {
@@ -48,6 +50,7 @@ func Send(
 		federation: federation,
 		haveEvents: make(map[string]*gomatrixserverlib.HeaderedEvent),
 		newEvents:  make(map[string]bool),
+		keyAPI:     keyAPI,
 	}
 
 	var txnEvents struct {
@@ -100,6 +103,7 @@ type txnReq struct {
 	context    context.Context
 	rsAPI      api.RoomserverInternalAPI
 	eduAPI     eduserverAPI.EDUServerInputAPI
+	keyAPI     keyapi.KeyInternalAPI
 	keys       gomatrixserverlib.JSONVerifier
 	federation txnFederationClient
 	// local cache of events for auth checks, etc - this may include events
@@ -308,12 +312,29 @@ func (t *txnReq) processEDUs(edus []gomatrixserverlib.EDU) {
 					}
 				}
 			}
+		case gomatrixserverlib.MDeviceListUpdate:
+			t.processDeviceListUpdate(e)
 		default:
 			util.GetLogger(t.context).WithField("type", e.Type).Warn("unhandled edu")
 		}
 	}
 }
 
+func (t *txnReq) processDeviceListUpdate(e gomatrixserverlib.EDU) {
+	var payload gomatrixserverlib.DeviceListUpdateEvent
+	if err := json.Unmarshal(e.Content, &payload); err != nil {
+		util.GetLogger(t.context).WithError(err).Error("Failed to unmarshal device list update event")
+		return
+	}
+	var inputRes keyapi.InputDeviceListUpdateResponse
+	t.keyAPI.InputDeviceListUpdate(context.Background(), &keyapi.InputDeviceListUpdateRequest{
+		Event: payload,
+	}, &inputRes)
+	if inputRes.Error != nil {
+		util.GetLogger(t.context).WithError(inputRes.Error).WithField("user_id", payload.UserID).Error("failed to InputDeviceListUpdate")
+	}
+}
+
 func (t *txnReq) processEvent(e gomatrixserverlib.Event, isInboundTxn bool) error {
 	prevEventIDs := e.PrevEventIDs()
 
diff --git a/keyserver/api/api.go b/keyserver/api/api.go
index c864b328..c3481a38 100644
--- a/keyserver/api/api.go
+++ b/keyserver/api/api.go
@@ -21,11 +21,14 @@ import (
 	"time"
 
 	userapi "github.com/matrix-org/dendrite/userapi/api"
+	"github.com/matrix-org/gomatrixserverlib"
 )
 
 type KeyInternalAPI interface {
 	// SetUserAPI assigns a user API to query when extracting device names.
 	SetUserAPI(i userapi.UserInternalAPI)
+	// InputDeviceListUpdate from a federated server EDU
+	InputDeviceListUpdate(ctx context.Context, req *InputDeviceListUpdateRequest, res *InputDeviceListUpdateResponse)
 	PerformUploadKeys(ctx context.Context, req *PerformUploadKeysRequest, res *PerformUploadKeysResponse)
 	// PerformClaimKeys claims one-time keys for use in pre-key messages
 	PerformClaimKeys(ctx context.Context, req *PerformClaimKeysRequest, res *PerformClaimKeysResponse)
@@ -200,3 +203,11 @@ type QueryDeviceMessagesResponse struct {
 	Devices  []DeviceMessage
 	Error    *KeyError
 }
+
+type InputDeviceListUpdateRequest struct {
+	Event gomatrixserverlib.DeviceListUpdateEvent
+}
+
+type InputDeviceListUpdateResponse struct {
+	Error *KeyError
+}
diff --git a/keyserver/internal/internal.go b/keyserver/internal/internal.go
index 474f30ff..d6e24566 100644
--- a/keyserver/internal/internal.go
+++ b/keyserver/internal/internal.go
@@ -38,12 +38,76 @@ type KeyInternalAPI struct {
 	FedClient  *gomatrixserverlib.FederationClient
 	UserAPI    userapi.UserInternalAPI
 	Producer   *producers.KeyChange
+	// A map from user_id to a mutex. Used when we are missing prev IDs so we don't make more than 1
+	// request to the remote server and race.
+	// TODO: Put in an LRU cache to bound growth
+	UserIDToMutex map[string]*sync.Mutex
+	Mutex         *sync.Mutex // protects UserIDToMutex
 }
 
 func (a *KeyInternalAPI) SetUserAPI(i userapi.UserInternalAPI) {
 	a.UserAPI = i
 }
 
+func (a *KeyInternalAPI) mutex(userID string) *sync.Mutex {
+	a.Mutex.Lock()
+	defer a.Mutex.Unlock()
+	if a.UserIDToMutex[userID] == nil {
+		a.UserIDToMutex[userID] = &sync.Mutex{}
+	}
+	return a.UserIDToMutex[userID]
+}
+
+func (a *KeyInternalAPI) InputDeviceListUpdate(
+	ctx context.Context, req *api.InputDeviceListUpdateRequest, res *api.InputDeviceListUpdateResponse,
+) {
+	mu := a.mutex(req.Event.UserID)
+	mu.Lock()
+	defer mu.Unlock()
+	// check if we have the prev IDs
+	exists, err := a.DB.PrevIDsExists(ctx, req.Event.UserID, req.Event.PrevID)
+	if err != nil {
+		res.Error = &api.KeyError{
+			Err: fmt.Sprintf("failed to check if prev ids exist: %s", err),
+		}
+		return
+	}
+
+	// if we haven't missed anything update the database and notify users
+	if exists {
+		keys := []api.DeviceMessage{
+			{
+				DeviceKeys: api.DeviceKeys{
+					DeviceID:    req.Event.DeviceID,
+					DisplayName: req.Event.DeviceDisplayName,
+					KeyJSON:     req.Event.Keys,
+					UserID:      req.Event.UserID,
+				},
+				StreamID: req.Event.StreamID,
+			},
+		}
+		err = a.DB.StoreRemoteDeviceKeys(ctx, keys)
+		if err != nil {
+			res.Error = &api.KeyError{
+				Err: fmt.Sprintf("failed to store remote device keys: %s", err),
+			}
+			return
+		}
+		// ALWAYS emit key changes when we've been poked over federation just in case
+		// this poke is important for something.
+		err = a.Producer.ProduceKeyChanges(keys)
+		if err != nil {
+			res.Error = &api.KeyError{
+				Err: fmt.Sprintf("failed to emit remote device key changes: %s", err),
+			}
+		}
+		return
+	}
+
+	// if we're missing an ID go and fetch it from the remote HS
+
+}
+
 func (a *KeyInternalAPI) QueryKeyChanges(ctx context.Context, req *api.QueryKeyChangesRequest, res *api.QueryKeyChangesResponse) {
 	if req.Partition < 0 {
 		req.Partition = a.Producer.DefaultPartition()
@@ -351,7 +415,7 @@ func (a *KeyInternalAPI) uploadLocalDeviceKeys(ctx context.Context, req *api.Per
 		return
 	}
 	// store the device keys and emit changes
-	err := a.DB.StoreDeviceKeys(ctx, keysToStore)
+	err := a.DB.StoreLocalDeviceKeys(ctx, keysToStore)
 	if err != nil {
 		res.Error = &api.KeyError{
 			Err: fmt.Sprintf("failed to store device keys: %s", err.Error()),
diff --git a/keyserver/inthttp/client.go b/keyserver/inthttp/client.go
index 93b19051..98200022 100644
--- a/keyserver/inthttp/client.go
+++ b/keyserver/inthttp/client.go
@@ -27,12 +27,13 @@ import (
 
 // HTTP paths for the internal HTTP APIs
 const (
-	PerformUploadKeysPath   = "/keyserver/performUploadKeys"
-	PerformClaimKeysPath    = "/keyserver/performClaimKeys"
-	QueryKeysPath           = "/keyserver/queryKeys"
-	QueryKeyChangesPath     = "/keyserver/queryKeyChanges"
-	QueryOneTimeKeysPath    = "/keyserver/queryOneTimeKeys"
-	QueryDeviceMessagesPath = "/keyserver/queryDeviceMessages"
+	InputDeviceListUpdatePath = "/keyserver/inputDeviceListUpdate"
+	PerformUploadKeysPath     = "/keyserver/performUploadKeys"
+	PerformClaimKeysPath      = "/keyserver/performClaimKeys"
+	QueryKeysPath             = "/keyserver/queryKeys"
+	QueryKeyChangesPath       = "/keyserver/queryKeyChanges"
+	QueryOneTimeKeysPath      = "/keyserver/queryOneTimeKeys"
+	QueryDeviceMessagesPath   = "/keyserver/queryDeviceMessages"
 )
 
 // NewKeyServerClient creates a KeyInternalAPI implemented by talking to a HTTP POST API.
@@ -58,6 +59,20 @@ type httpKeyInternalAPI struct {
 func (h *httpKeyInternalAPI) SetUserAPI(i userapi.UserInternalAPI) {
 	// no-op: doesn't need it
 }
+func (h *httpKeyInternalAPI) InputDeviceListUpdate(
+	ctx context.Context, req *api.InputDeviceListUpdateRequest, res *api.InputDeviceListUpdateResponse,
+) {
+	span, ctx := opentracing.StartSpanFromContext(ctx, "InputDeviceListUpdate")
+	defer span.Finish()
+
+	apiURL := h.apiURL + InputDeviceListUpdatePath
+	err := httputil.PostJSON(ctx, span, h.httpClient, apiURL, req, res)
+	if err != nil {
+		res.Error = &api.KeyError{
+			Err: err.Error(),
+		}
+	}
+}
 
 func (h *httpKeyInternalAPI) PerformClaimKeys(
 	ctx context.Context,
diff --git a/keyserver/inthttp/server.go b/keyserver/inthttp/server.go
index f0cd3038..7dfaed2e 100644
--- a/keyserver/inthttp/server.go
+++ b/keyserver/inthttp/server.go
@@ -25,6 +25,17 @@ import (
 )
 
 func AddRoutes(internalAPIMux *mux.Router, s api.KeyInternalAPI) {
+	internalAPIMux.Handle(InputDeviceListUpdatePath,
+		httputil.MakeInternalAPI("inputDeviceListUpdate", func(req *http.Request) util.JSONResponse {
+			request := api.InputDeviceListUpdateRequest{}
+			response := api.InputDeviceListUpdateResponse{}
+			if err := json.NewDecoder(req.Body).Decode(&request); err != nil {
+				return util.MessageResponse(http.StatusBadRequest, err.Error())
+			}
+			s.InputDeviceListUpdate(req.Context(), &request, &response)
+			return util.JSONResponse{Code: http.StatusOK, JSON: &response}
+		}),
+	)
 	internalAPIMux.Handle(PerformClaimKeysPath,
 		httputil.MakeInternalAPI("performClaimKeys", func(req *http.Request) util.JSONResponse {
 			request := api.PerformClaimKeysRequest{}
diff --git a/keyserver/keyserver.go b/keyserver/keyserver.go
index 36bedf34..79d9cec9 100644
--- a/keyserver/keyserver.go
+++ b/keyserver/keyserver.go
@@ -15,6 +15,8 @@
 package keyserver
 
 import (
+	"sync"
+
 	"github.com/Shopify/sarama"
 	"github.com/gorilla/mux"
 	"github.com/matrix-org/dendrite/internal/config"
@@ -51,9 +53,11 @@ func NewInternalAPI(
 		DB:       db,
 	}
 	return &internal.KeyInternalAPI{
-		DB:         db,
-		ThisServer: cfg.Matrix.ServerName,
-		FedClient:  fedClient,
-		Producer:   keyChangeProducer,
+		DB:            db,
+		ThisServer:    cfg.Matrix.ServerName,
+		FedClient:     fedClient,
+		Producer:      keyChangeProducer,
+		Mutex:         &sync.Mutex{},
+		UserIDToMutex: make(map[string]*sync.Mutex),
 	}
 }
diff --git a/keyserver/storage/interface.go b/keyserver/storage/interface.go
index 11284d86..f67bbf71 100644
--- a/keyserver/storage/interface.go
+++ b/keyserver/storage/interface.go
@@ -35,11 +35,18 @@ type Database interface {
 	// DeviceKeysJSON populates the KeyJSON for the given keys. If any proided `keys` have a `KeyJSON` or `StreamID` already then it will be replaced.
 	DeviceKeysJSON(ctx context.Context, keys []api.DeviceMessage) error
 
-	// StoreDeviceKeys persists the given keys. Keys with the same user ID and device ID will be replaced. An empty KeyJSON removes the key
+	// StoreLocalDeviceKeys persists the given keys. Keys with the same user ID and device ID will be replaced. An empty KeyJSON removes the key
 	// for this (user, device).
 	// The `StreamID` for each message is set on successful insertion. In the event the key already exists, the existing StreamID is set.
 	// Returns an error if there was a problem storing the keys.
-	StoreDeviceKeys(ctx context.Context, keys []api.DeviceMessage) error
+	StoreLocalDeviceKeys(ctx context.Context, keys []api.DeviceMessage) error
+
+	// StoreRemoteDeviceKeys persists the given keys. Keys with the same user ID and device ID will be replaced. An empty KeyJSON removes the key
+	// for this (user, device). Does not modify the stream ID for keys.
+	StoreRemoteDeviceKeys(ctx context.Context, keys []api.DeviceMessage) error
+
+	// PrevIDsExists returns true if all prev IDs exist for this user.
+	PrevIDsExists(ctx context.Context, userID string, prevIDs []int) (bool, error)
 
 	// DeviceKeysForUser returns the device keys for the device IDs given. If the length of deviceIDs is 0, all devices are selected.
 	// If there are some missing keys, they are omitted from the returned slice. There is no ordering on the returned slice.
diff --git a/keyserver/storage/postgres/device_keys_table.go b/keyserver/storage/postgres/device_keys_table.go
index e1b4e947..d321860d 100644
--- a/keyserver/storage/postgres/device_keys_table.go
+++ b/keyserver/storage/postgres/device_keys_table.go
@@ -19,6 +19,7 @@ import (
 	"database/sql"
 	"time"
 
+	"github.com/lib/pq"
 	"github.com/matrix-org/dendrite/internal"
 	"github.com/matrix-org/dendrite/keyserver/api"
 	"github.com/matrix-org/dendrite/keyserver/storage/tables"
@@ -56,12 +57,16 @@ const selectBatchDeviceKeysSQL = "" +
 const selectMaxStreamForUserSQL = "" +
 	"SELECT MAX(stream_id) FROM keyserver_device_keys WHERE user_id=$1"
 
+const countStreamIDsForUserSQL = "" +
+	"SELECT COUNT(*) FROM keyserver_device_keys WHERE user_id=$1 AND stream_id = ANY($2)"
+
 type deviceKeysStatements struct {
 	db                         *sql.DB
 	upsertDeviceKeysStmt       *sql.Stmt
 	selectDeviceKeysStmt       *sql.Stmt
 	selectBatchDeviceKeysStmt  *sql.Stmt
 	selectMaxStreamForUserStmt *sql.Stmt
+	countStreamIDsForUserStmt  *sql.Stmt
 }
 
 func NewPostgresDeviceKeysTable(db *sql.DB) (tables.DeviceKeys, error) {
@@ -84,6 +89,9 @@ func NewPostgresDeviceKeysTable(db *sql.DB) (tables.DeviceKeys, error) {
 	if s.selectMaxStreamForUserStmt, err = db.Prepare(selectMaxStreamForUserSQL); err != nil {
 		return nil, err
 	}
+	if s.countStreamIDsForUserStmt, err = db.Prepare(countStreamIDsForUserSQL); err != nil {
+		return nil, err
+	}
 	return s, nil
 }
 
@@ -115,6 +123,19 @@ func (s *deviceKeysStatements) SelectMaxStreamIDForUser(ctx context.Context, txn
 	return
 }
 
+func (s *deviceKeysStatements) CountStreamIDsForUser(ctx context.Context, userID string, streamIDs []int64) (int, error) {
+	// nullable if there are no results
+	var count sql.NullInt32
+	err := s.countStreamIDsForUserStmt.QueryRowContext(ctx, userID, pq.Int64Array(streamIDs)).Scan(&count)
+	if err != nil {
+		return 0, err
+	}
+	if count.Valid {
+		return int(count.Int32), nil
+	}
+	return 0, nil
+}
+
 func (s *deviceKeysStatements) InsertDeviceKeys(ctx context.Context, txn *sql.Tx, keys []api.DeviceMessage) error {
 	for _, key := range keys {
 		now := time.Now().Unix()
diff --git a/keyserver/storage/shared/storage.go b/keyserver/storage/shared/storage.go
index e78ee943..78729774 100644
--- a/keyserver/storage/shared/storage.go
+++ b/keyserver/storage/shared/storage.go
@@ -47,7 +47,25 @@ func (d *Database) DeviceKeysJSON(ctx context.Context, keys []api.DeviceMessage)
 	return d.DeviceKeysTable.SelectDeviceKeysJSON(ctx, keys)
 }
 
-func (d *Database) StoreDeviceKeys(ctx context.Context, keys []api.DeviceMessage) error {
+func (d *Database) PrevIDsExists(ctx context.Context, userID string, prevIDs []int) (bool, error) {
+	sids := make([]int64, len(prevIDs))
+	for i := range prevIDs {
+		sids[i] = int64(prevIDs[i])
+	}
+	count, err := d.DeviceKeysTable.CountStreamIDsForUser(ctx, userID, sids)
+	if err != nil {
+		return false, err
+	}
+	return count == len(prevIDs), nil
+}
+
+func (d *Database) StoreRemoteDeviceKeys(ctx context.Context, keys []api.DeviceMessage) error {
+	return sqlutil.WithTransaction(d.DB, func(txn *sql.Tx) error {
+		return d.DeviceKeysTable.InsertDeviceKeys(ctx, txn, keys)
+	})
+}
+
+func (d *Database) StoreLocalDeviceKeys(ctx context.Context, keys []api.DeviceMessage) error {
 	// work out the latest stream IDs for each user
 	userIDToStreamID := make(map[string]int)
 	for _, k := range keys {
diff --git a/keyserver/storage/sqlite3/device_keys_table.go b/keyserver/storage/sqlite3/device_keys_table.go
index 900d1238..15d9c775 100644
--- a/keyserver/storage/sqlite3/device_keys_table.go
+++ b/keyserver/storage/sqlite3/device_keys_table.go
@@ -17,6 +17,7 @@ package sqlite3
 import (
 	"context"
 	"database/sql"
+	"strings"
 	"time"
 
 	"github.com/matrix-org/dendrite/internal"
@@ -53,6 +54,9 @@ const selectBatchDeviceKeysSQL = "" +
 const selectMaxStreamForUserSQL = "" +
 	"SELECT MAX(stream_id) FROM keyserver_device_keys WHERE user_id=$1"
 
+const countStreamIDsForUserSQL = "" +
+	"SELECT COUNT(*) FROM keyserver_device_keys WHERE user_id=$1 AND stream_id IN ($2)"
+
 type deviceKeysStatements struct {
 	db                         *sql.DB
 	writer                     *sqlutil.TransactionWriter
@@ -143,6 +147,25 @@ func (s *deviceKeysStatements) SelectMaxStreamIDForUser(ctx context.Context, txn
 	return
 }
 
+func (s *deviceKeysStatements) CountStreamIDsForUser(ctx context.Context, userID string, streamIDs []int64) (int, error) {
+	iStreamIDs := make([]interface{}, len(streamIDs)+1)
+	iStreamIDs[0] = userID
+	for i := range streamIDs {
+		iStreamIDs[i+1] = streamIDs[i]
+	}
+	query := strings.Replace(countStreamIDsForUserSQL, "($2)", sqlutil.QueryVariadicOffset(len(streamIDs), 1), 1)
+	// nullable if there are no results
+	var count sql.NullInt32
+	err := s.db.QueryRowContext(ctx, query, iStreamIDs...).Scan(&count)
+	if err != nil {
+		return 0, err
+	}
+	if count.Valid {
+		return int(count.Int32), nil
+	}
+	return 0, nil
+}
+
 func (s *deviceKeysStatements) InsertDeviceKeys(ctx context.Context, txn *sql.Tx, keys []api.DeviceMessage) error {
 	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 		for _, key := range keys {
diff --git a/keyserver/storage/storage_test.go b/keyserver/storage/storage_test.go
index 949d9dd6..ec1b299f 100644
--- a/keyserver/storage/storage_test.go
+++ b/keyserver/storage/storage_test.go
@@ -126,15 +126,15 @@ func TestDeviceKeysStreamIDGeneration(t *testing.T) {
 			// StreamID: 2 as this is a 2nd device key
 		},
 	}
-	MustNotError(t, db.StoreDeviceKeys(ctx, msgs))
+	MustNotError(t, db.StoreLocalDeviceKeys(ctx, msgs))
 	if msgs[0].StreamID != 1 {
-		t.Fatalf("Expected StoreDeviceKeys to set StreamID=1 but got %d", msgs[0].StreamID)
+		t.Fatalf("Expected StoreLocalDeviceKeys to set StreamID=1 but got %d", msgs[0].StreamID)
 	}
 	if msgs[1].StreamID != 1 {
-		t.Fatalf("Expected StoreDeviceKeys to set StreamID=1 (different user) but got %d", msgs[1].StreamID)
+		t.Fatalf("Expected StoreLocalDeviceKeys to set StreamID=1 (different user) but got %d", msgs[1].StreamID)
 	}
 	if msgs[2].StreamID != 2 {
-		t.Fatalf("Expected StoreDeviceKeys to set StreamID=2 (another device) but got %d", msgs[2].StreamID)
+		t.Fatalf("Expected StoreLocalDeviceKeys to set StreamID=2 (another device) but got %d", msgs[2].StreamID)
 	}
 
 	// updating a device sets the next stream ID for that user
@@ -148,9 +148,9 @@ func TestDeviceKeysStreamIDGeneration(t *testing.T) {
 			// StreamID: 3
 		},
 	}
-	MustNotError(t, db.StoreDeviceKeys(ctx, msgs))
+	MustNotError(t, db.StoreLocalDeviceKeys(ctx, msgs))
 	if msgs[0].StreamID != 3 {
-		t.Fatalf("Expected StoreDeviceKeys to set StreamID=3 (new key same device) but got %d", msgs[0].StreamID)
+		t.Fatalf("Expected StoreLocalDeviceKeys to set StreamID=3 (new key same device) but got %d", msgs[0].StreamID)
 	}
 
 	// Querying for device keys returns the latest stream IDs
diff --git a/keyserver/storage/tables/interface.go b/keyserver/storage/tables/interface.go
index 65da3310..ac932d56 100644
--- a/keyserver/storage/tables/interface.go
+++ b/keyserver/storage/tables/interface.go
@@ -35,6 +35,7 @@ type DeviceKeys interface {
 	SelectDeviceKeysJSON(ctx context.Context, keys []api.DeviceMessage) error
 	InsertDeviceKeys(ctx context.Context, txn *sql.Tx, keys []api.DeviceMessage) error
 	SelectMaxStreamIDForUser(ctx context.Context, txn *sql.Tx, userID string) (streamID int32, err error)
+	CountStreamIDsForUser(ctx context.Context, userID string, streamIDs []int64) (int, error)
 	SelectBatchDeviceKeys(ctx context.Context, userID string, deviceIDs []string) ([]api.DeviceMessage, error)
 }
 
diff --git a/syncapi/internal/keychange_test.go b/syncapi/internal/keychange_test.go
index cc33c738..6765fa65 100644
--- a/syncapi/internal/keychange_test.go
+++ b/syncapi/internal/keychange_test.go
@@ -44,6 +44,9 @@ func (k *mockKeyAPI) QueryOneTimeKeys(ctx context.Context, req *keyapi.QueryOneT
 }
 func (k *mockKeyAPI) QueryDeviceMessages(ctx context.Context, req *keyapi.QueryDeviceMessagesRequest, res *keyapi.QueryDeviceMessagesResponse) {
 
+}
+func (k *mockKeyAPI) InputDeviceListUpdate(ctx context.Context, req *keyapi.InputDeviceListUpdateRequest, res *keyapi.InputDeviceListUpdateResponse) {
+
 }
 
 type mockCurrentStateAPI struct {