diff --git a/data/event-schemas/schema/m.room.avatar.yaml b/data/event-schemas/schema/m.room.avatar.yaml
index 7d4b90b15..f48053e91 100644
--- a/data/event-schemas/schema/m.room.avatar.yaml
+++ b/data/event-schemas/schema/m.room.avatar.yaml
@@ -10,8 +10,13 @@ properties:
           - $ref: core-event-schema/msgtype_infos/image_info.yaml
         description: Metadata about the image referred to in `url`.
       url:
-        description: The URL to the image.
+        description: |-
+          The URL to the image.
+
+          Despite this field being required, it is allowed to be `null` to cover
+          the case of an event that unsets a previously-set avatar.
         type: string
+        nullable: true
     required:
       - url
     type: object