diff --git a/dendrite-sample.yaml b/dendrite-sample.yaml
index 7affc2599..f338dd431 100644
--- a/dendrite-sample.yaml
+++ b/dendrite-sample.yaml
@@ -325,6 +325,10 @@ user_api:
   auto_join_rooms:
   #  - "#main:matrix.org"
 
+  # The number of device list updater workers to start. Defaults to 8.
+  # This only needs updating if the "InputDeviceListUpdate" stream keeps growing indefinitely.
+  # worker_count: 8
+
 # Configuration for Opentracing.
 # See https://github.com/matrix-org/dendrite/tree/master/docs/tracing for information on
 # how this works and how to set it up.
diff --git a/setup/config/config_userapi.go b/setup/config/config_userapi.go
index e64a3910c..108de0034 100644
--- a/setup/config/config_userapi.go
+++ b/setup/config/config_userapi.go
@@ -21,6 +21,10 @@ type UserAPI struct {
 	// Users who register on this homeserver will automatically
 	// be joined to the rooms listed under this option.
 	AutoJoinRooms []string `yaml:"auto_join_rooms"`
+
+	// The number of workers to start for the DeviceListUpdater.
+	// Setting this too low may result in the "InputDeviceListUpdate" growing forever.
+	WorkerCount int `yaml:"worker_count"`
 }
 
 const DefaultOpenIDTokenLifetimeMS = 3600000 // 60 minutes
@@ -28,6 +32,7 @@ const DefaultOpenIDTokenLifetimeMS = 3600000 // 60 minutes
 func (c *UserAPI) Defaults(opts DefaultOpts) {
 	c.BCryptCost = bcrypt.DefaultCost
 	c.OpenIDTokenLifetimeMS = DefaultOpenIDTokenLifetimeMS
+	c.WorkerCount = 8
 	if opts.Generate {
 		if !opts.SingleDatabase {
 			c.AccountDatabase.ConnectionString = "file:userapi_accounts.db"
diff --git a/userapi/userapi.go b/userapi/userapi.go
index 7081db841..34bf119a0 100644
--- a/userapi/userapi.go
+++ b/userapi/userapi.go
@@ -100,7 +100,7 @@ func NewInternalAPI(
 		FedClient:            fedClient,
 	}
 
-	updater := internal.NewDeviceListUpdater(processContext, keyDB, userAPI, keyChangeProducer, fedClient, 8, rsAPI, dendriteCfg.Global.ServerName, enableMetrics) // 8 workers TODO: configurable
+	updater := internal.NewDeviceListUpdater(processContext, keyDB, userAPI, keyChangeProducer, fedClient, dendriteCfg.UserAPI.WorkerCount, rsAPI, dendriteCfg.Global.ServerName, enableMetrics)
 	userAPI.Updater = updater
 	// Remove users which we don't share a room with anymore
 	if err := updater.CleanUp(); err != nil {