diff --git a/src/github.com/matrix-org/dendrite/clientapi/common/common.go b/src/github.com/matrix-org/dendrite/clientapi/common/common.go
index e6e8e8acb..cbc94a6f5 100644
--- a/src/github.com/matrix-org/dendrite/clientapi/common/common.go
+++ b/src/github.com/matrix-org/dendrite/clientapi/common/common.go
@@ -2,37 +2,12 @@ package common
 
 import (
 	"encoding/json"
-	"fmt"
+	"net/http"
+
 	"github.com/matrix-org/dendrite/clientapi/jsonerror"
 	"github.com/matrix-org/util"
-	"net/http"
-	"strings"
 )
 
-// UserID represents a parsed User ID string
-type UserID struct {
-	Domain    string
-	Localpart string
-}
-
-// UserIDFromString creates a UserID from an input string. Returns an error if
-// the string is not a valid user ID.
-func UserIDFromString(id string) (uid UserID, err error) {
-	// https://github.com/matrix-org/synapse/blob/v0.19.2/synapse/types.py#L92
-	if len(id) == 0 || id[0] != '@' {
-		err = fmt.Errorf("user id must start with '@'")
-		return
-	}
-	parts := strings.SplitN(id[1:], ":", 2)
-	if len(parts) != 2 {
-		err = fmt.Errorf("user id must be in the form @localpart:domain")
-		return
-	}
-	uid.Localpart = parts[0]
-	uid.Domain = parts[1]
-	return
-}
-
 // UnmarshalJSONRequest into the given interface pointer. Returns an error JSON response if
 // there was a problem unmarshalling. Calling this function consumes the request body.
 func UnmarshalJSONRequest(req *http.Request, iface interface{}) *util.JSONResponse {
diff --git a/src/github.com/matrix-org/dendrite/clientapi/writers/createroom.go b/src/github.com/matrix-org/dendrite/clientapi/writers/createroom.go
index d95199109..edf2e7e15 100644
--- a/src/github.com/matrix-org/dendrite/clientapi/writers/createroom.go
+++ b/src/github.com/matrix-org/dendrite/clientapi/writers/createroom.go
@@ -35,10 +35,22 @@ func (r createRoomRequest) Validate() *util.JSONResponse {
 		}
 	}
 	for _, userID := range r.Invite {
-		if _, err := common.UserIDFromString(userID); err != nil {
+		// TODO: We should put user ID parsing code into gomatrixserverlib and use that instead
+		//       (see https://github.com/matrix-org/gomatrixserverlib/blob/3394e7c7003312043208aa73727d2256eea3d1f6/eventcontent.go#L347 )
+		//       It should be a struct (with pointers into a single string to avoid copying) and
+		//       we should update all refs to use UserID types rather than strings.
+		// https://github.com/matrix-org/synapse/blob/v0.19.2/synapse/types.py#L92
+		if len(userID) == 0 || userID[0] != '@' {
 			return &util.JSONResponse{
 				Code: 400,
-				JSON: jsonerror.BadJSON("Entries in 'invite' must be valid user IDs"),
+				JSON: jsonerror.BadJSON("user id must start with '@'"),
+			}
+		}
+		parts := strings.SplitN(userID[1:], ":", 2)
+		if len(parts) != 2 {
+			return &util.JSONResponse{
+				Code: 400,
+				JSON: jsonerror.BadJSON("user id must be in the form @localpart:domain"),
 			}
 		}
 	}