diff --git a/tests/federation_device_list_update_test.go b/tests/federation_device_list_update_test.go
new file mode 100644
index 00000000..15bb2303
--- /dev/null
+++ b/tests/federation_device_list_update_test.go
@@ -0,0 +1,160 @@
+package tests
+
+import (
+	"fmt"
+	"reflect"
+	"sort"
+	"testing"
+	"time"
+
+	"github.com/matrix-org/complement"
+	"github.com/matrix-org/complement/client"
+	"github.com/matrix-org/complement/helpers"
+	"github.com/tidwall/gjson"
+)
+
+// Test that device list updates can go from one homeserver to another.
+func TestDeviceListsUpdateOverFederation(t *testing.T) {
+	deployment := complement.Deploy(t, 2)
+	defer deployment.Destroy(t)
+
+	syncHasDeviceListChange := func(changed []string, left []string) client.SyncCheckOpt {
+		sort.Strings(changed)
+		sort.Strings(left)
+		return func(clientUserID string, topLevelSyncJSON gjson.Result) error {
+			dl := topLevelSyncJSON.Get("device_lists")
+			changedJSON := dl.Get("changed").Array()
+			leftJSON := dl.Get("left").Array()
+			gotChanged := make([]string, len(changedJSON))
+			gotLeft := make([]string, len(leftJSON))
+			for i := range gotChanged {
+				gotChanged[i] = changedJSON[i].Str
+			}
+			for i := range gotLeft {
+				gotLeft[i] = leftJSON[i].Str
+			}
+			sort.Strings(gotChanged)
+			sort.Strings(gotLeft)
+			changedMatch := reflect.DeepEqual(changed, gotChanged)
+			leftMatch := reflect.DeepEqual(left, gotLeft)
+			if changedMatch && leftMatch {
+				return nil
+			}
+			return fmt.Errorf("syncHasDeviceListChange: got changed %v want %v, got left %v want %v", gotChanged, changed, gotLeft, left)
+		}
+	}
+
+	testCases := []struct {
+		name            string
+		makeUnreachable func(t *testing.T)
+		makeReachable   func(t *testing.T)
+	}{
+		{
+			name:            "good connectivity",
+			makeUnreachable: func(t *testing.T) {},
+			makeReachable:   func(t *testing.T) {},
+		},
+		{
+			// cut networking but keep in-memory state
+			name: "interrupted connectivity",
+			makeUnreachable: func(t *testing.T) {
+				deployment.StopServer(t, "hs2")
+			},
+			makeReachable: func(t *testing.T) {
+				deployment.StartServer(t, "hs2")
+			},
+		},
+		{
+			// interesting because this nukes memory
+			name: "stopped server",
+			makeUnreachable: func(t *testing.T) {
+				deployment.StopServer(t, "hs2")
+			},
+			makeReachable: func(t *testing.T) {
+				// kick over the sending server first to see if the server
+				// remembers to resend on startup
+				deployment.StopServer(t, "hs1")
+				deployment.StartServer(t, "hs1")
+				// now make the receiving server reachable.
+				deployment.StartServer(t, "hs2")
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			alice := deployment.Register(t, "hs1", helpers.RegistrationOpts{
+				LocalpartSuffix: "alice",
+				Password:        "this is alices password",
+			})
+			bob := deployment.Register(t, "hs2", helpers.RegistrationOpts{
+				LocalpartSuffix: "bob",
+			})
+			// they must share a room to get device list updates
+			roomID := alice.MustCreateRoom(t, map[string]interface{}{
+				"preset": "private_chat",
+				"invite": []string{bob.UserID},
+				// we strictly don't need to make this an encrypted room, but there are some
+				// issues which state that we should only share device list updates for
+				// users in shared encrypted rooms, so let's ensure we do that.
+				// See https://github.com/matrix-org/synapse/issues/7524
+				"initial_state": []map[string]interface{}{
+					{
+						"type":      "m.room.encryption",
+						"state_key": "",
+						"content": map[string]interface{}{
+							"algorithm": "m.megolm.v1.aes-sha2",
+						},
+					},
+				},
+			})
+			// it might take a while for retries, so keep on syncing!
+			bob.SyncUntilTimeout = 50 * time.Second
+			_, aliceSince := alice.MustSync(t, client.SyncReq{TimeoutMillis: "0"})
+			bobSince := bob.MustSyncUntil(t, client.SyncReq{TimeoutMillis: "0"}, client.SyncInvitedTo(bob.UserID, roomID))
+
+			bob.MustJoinRoom(t, roomID, []string{"hs1"})
+
+			// both alice and bob should see device list updates for each other
+			aliceSince = alice.MustSyncUntil(
+				t, client.SyncReq{TimeoutMillis: "1000", Since: aliceSince},
+				syncHasDeviceListChange([]string{bob.UserID}, []string{}),
+			)
+			bobSince = bob.MustSyncUntil(
+				t, client.SyncReq{TimeoutMillis: "1000", Since: bobSince},
+				// bob is in this list because... his other devices may need to know.
+				syncHasDeviceListChange([]string{alice.UserID, bob.UserID}, []string{}),
+			)
+
+			// now federation is going to be interrupted...
+			tc.makeUnreachable(t)
+
+			// ..and alice logs in on a new device!
+			alice2 := deployment.Login(t, "hs1", alice, helpers.LoginOpts{
+				DeviceID: "NEW_DEVICE",
+				Password: "this is alices password",
+			})
+			deviceKeys, oneTimeKeys := alice2.MustGenerateOneTimeKeys(t, 1)
+			alice2.MustDo(t, "POST", []string{"_matrix", "client", "v3", "keys", "upload"}, client.WithJSONBody(t, map[string]interface{}{
+				"device_keys":   deviceKeys,
+				"one_time_keys": oneTimeKeys,
+			}))
+
+			// now federation comes back online
+			tc.makeReachable(t)
+
+			// ensure alice sees her new device login
+			aliceSince = alice.MustSyncUntil(
+				t, client.SyncReq{TimeoutMillis: "1000", Since: aliceSince},
+				syncHasDeviceListChange([]string{alice.UserID}, []string{}),
+			)
+
+			// ensure bob sees the device list change
+			bobSince = bob.MustSyncUntil(
+				t, client.SyncReq{TimeoutMillis: "1000", Since: bobSince},
+				syncHasDeviceListChange([]string{alice.UserID}, []string{}),
+			)
+		})
+	}
+}