diff --git a/src/github.com/matrix-org/dendrite/clientapi/routing/register.go b/src/github.com/matrix-org/dendrite/clientapi/routing/register.go
index 107344c3..77e875ec 100644
--- a/src/github.com/matrix-org/dendrite/clientapi/routing/register.go
+++ b/src/github.com/matrix-org/dendrite/clientapi/routing/register.go
@@ -381,8 +381,9 @@ func Register(
 	}
 
 	// Make sure normal user isn't registering under an exclusive application
-	// service namespace
+	// service namespace. Skip this check if no app services are registered.
 	if r.Auth.Type != "m.login.application_service" &&
+		len(cfg.Derived.ApplicationServices) != 0 &&
 		cfg.Derived.ExclusiveApplicationServicesUsernameRegexp.MatchString(r.Username) {
 		return util.JSONResponse{
 			Code: 400,
diff --git a/src/github.com/matrix-org/dendrite/common/config/appservice.go b/src/github.com/matrix-org/dendrite/common/config/appservice.go
index 72efafac..b57e9d06 100644
--- a/src/github.com/matrix-org/dendrite/common/config/appservice.go
+++ b/src/github.com/matrix-org/dendrite/common/config/appservice.go
@@ -113,6 +113,12 @@ func setupRegexps(cfg *Dendrite) {
 	// regex and deny access if it isn't from an application service
 	exclusiveUsernames := strings.Join(exclusiveUsernameStrings, "|")
 
+	// If there are no exclusive username regexes, compile string so that it
+	// will not match any valid usernames
+	if exclusiveUsernames == "" {
+		exclusiveUsernames = "^$"
+	}
+
 	// TODO: Aliases and rooms. Needed?
 	//exclusiveAliases := strings.Join(exclusiveAliasStrings, "|")
 	//exclusiveRooms := strings.Join(exclusiveRoomStrings, "|")