diff --git a/scl.py b/scl.py
index 4f1a4db..e72a5de 100644
--- a/scl.py
+++ b/scl.py
@@ -222,7 +222,7 @@ def do_initial_post(
             map_image.save(map_image_file, format="WebP", method=6)
             map_media_post = mastodon_client.media_post(
                 map_image_file.getvalue(),
-                mime_type="image/png",
+                mime_type="image/webp",
                 description=alt_text,
             )
         map_media_post_id = map_media_post["id"]