diff --git a/data/event-schemas/schema/m.room.message$m.video.yaml b/data/event-schemas/schema/m.room.message$m.video.yaml
index 6d8c49e8..5ff9c250 100644
--- a/data/event-schemas/schema/m.room.message$m.video.yaml
+++ b/data/event-schemas/schema/m.room.message$m.video.yaml
@@ -54,6 +54,8 @@ properties:
               The URL (typically [`mxc://` URI](/client-server-api/#matrix-content-mxc-uris)) to an image thumbnail of
               the video clip. Only present if the thumbnail is unencrypted.
             type: string
+            format: mx-mxc-uri
+            pattern: "^mxc:\\/\\/"
           thumbnail_file:
             description: |-
               Information on the encrypted thumbnail file, as specified in
@@ -76,6 +78,8 @@ properties:
           Required if the file is unencrypted. The URL (typically [`mxc://` URI](/client-server-api/#matrix-content-mxc-uris))
           to the video clip.
         type: string
+        format: mx-mxc-uri
+        pattern: "^mxc:\\/\\/"
       file:
         description: |-
           Required if the file is encrypted. Information on the encrypted