diff --git a/clientapi/routing/directory.go b/clientapi/routing/directory.go
index e408c264..ac355b5d 100644
--- a/clientapi/routing/directory.go
+++ b/clientapi/routing/directory.go
@@ -139,11 +139,17 @@ func SetLocalAlias(
 	// TODO: This code should eventually be refactored with:
 	// 1. The new method for checking for things matching an AS's namespace
 	// 2. Using an overall Regex object for all AS's just like we did for usernames
-
+	reqUserID, _, err := gomatrixserverlib.SplitID('@', device.UserID)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.BadJSON("User ID must be in the form '@localpart:domain'"),
+		}
+	}
 	for _, appservice := range cfg.Derived.ApplicationServices {
 		// Don't prevent AS from creating aliases in its own namespace
 		// Note that Dendrite uses SenderLocalpart as UserID for AS users
-		if device.UserID != appservice.SenderLocalpart {
+		if reqUserID != appservice.SenderLocalpart {
 			if aliasNamespaces, ok := appservice.NamespaceMap["aliases"]; ok {
 				for _, namespace := range aliasNamespaces {
 					if namespace.Exclusive && namespace.RegexpObject.MatchString(alias) {
diff --git a/sytest-blacklist b/sytest-blacklist
index 0cdfebcc..cee2406e 100644
--- a/sytest-blacklist
+++ b/sytest-blacklist
@@ -24,6 +24,7 @@ Local device key changes get to remote servers with correct prev_id
 
 # Flakey
 Local device key changes appear in /keys/changes
+/context/ with lazy_load_members filter works
 
 # we don't support groups
 Remove group category
@@ -32,6 +33,8 @@ Remove group role
 # Flakey
 AS-ghosted users can use rooms themselves
 /context/ with lazy_load_members filter works
+AS-ghosted users can use rooms via AS
+Events in rooms with AS-hosted room aliases are sent to AS server
 
 # Flakey, need additional investigation
 Messages that notify from another user increment notification_count
diff --git a/sytest-whitelist b/sytest-whitelist
index 377425c9..6c4745b3 100644
--- a/sytest-whitelist
+++ b/sytest-whitelist
@@ -648,7 +648,6 @@ Device list doesn't change if remote server is down
 /context/ on joined room works
 /context/ on non world readable room does not work
 /context/ returns correct number of events
-
 GET /rooms/:room_id/messages lazy loads members correctly
 Can query remote device keys using POST after notification
 Device deletion propagates over federation
@@ -659,8 +658,9 @@ registration accepts non-ascii passwords
 registration with inhibit_login inhibits login
 The operation must be consistent through an interactive authentication session
 Multiple calls to /sync should not cause 500 errors
-
 Canonical alias can be set
 Canonical alias can include alt_aliases
 Can delete canonical alias
 Multiple calls to /sync should not cause 500 errors
+AS can make room aliases
+Accesing an AS-hosted room alias asks the AS server