diff --git a/event-schemas/schema/m.room.member b/event-schemas/schema/m.room.member
index 055a1945..f9aa5051 100644
--- a/event-schemas/schema/m.room.member
+++ b/event-schemas/schema/m.room.member
@@ -28,7 +28,7 @@ properties:
       displayname:
         description: 'The display name for this user, if any. This is added by the homeserver.'
         type:
-          - string
+          - "string"
           - "null"
       membership:
         description: The membership state of the user.