diff --git a/app/javascript/mastodon/features/alt_text_modal/index.tsx b/app/javascript/mastodon/features/alt_text_modal/index.tsx
index fc00e60a51d..fafd4609477 100644
--- a/app/javascript/mastodon/features/alt_text_modal/index.tsx
+++ b/app/javascript/mastodon/features/alt_text_modal/index.tsx
@@ -54,7 +54,8 @@ const messages = defineMessages({
   },
 });
 
-const MAX_LENGTH = 1500;
+// TODO: use `description_limit` from the `/api/v2/instance` response
+const MAX_LENGTH = 10000;
 
 type FocalPoint = [number, number];
 
diff --git a/app/models/media_attachment.rb b/app/models/media_attachment.rb
index 1a65a447529..5ba5277d33d 100644
--- a/app/models/media_attachment.rb
+++ b/app/models/media_attachment.rb
@@ -40,7 +40,7 @@ class MediaAttachment < ApplicationRecord
 
   SHORTCODE_LENGTH = 19
 
-  MAX_DESCRIPTION_LENGTH = 1_500
+  MAX_DESCRIPTION_LENGTH = 10_000
   MAX_DESCRIPTION_HARD_LENGTH_LIMIT = 10_000
 
   IMAGE_LIMIT = 16.megabytes