diff --git a/tildes/development.ini b/tildes/development.ini
index f66f08d..5b608fa 100644
--- a/tildes/development.ini
+++ b/tildes/development.ini
@@ -42,5 +42,4 @@ webassets.auto_build = false
 webassets.base_dir = %(here)s/static
 webassets.base_url = /
 webassets.cache = false
-webassets.manifest = json
-
+webassets.manifest = json
\ No newline at end of file
diff --git a/tildes/tildes/views/api/web/user.py b/tildes/tildes/views/api/web/user.py
index af473bf..a97514e 100644
--- a/tildes/tildes/views/api/web/user.py
+++ b/tildes/tildes/views/api/web/user.py
@@ -8,8 +8,7 @@ import string
 from typing import Optional
 
 from marshmallow import ValidationError
-from marshmallow.fields import String
-from marshmallow.fields import Int
+from marshmallow.fields import String, Int
 from pyramid.httpexceptions import (
     HTTPForbidden,
     HTTPUnauthorized,
@@ -273,6 +272,22 @@ def patch_change_collapse_old_comments(request: Request) -> Response:
     return IC_NOOP
 
 
+@ic_view_config(
+    route_name="user",
+    request_method="PATCH",
+    request_param="ic-trigger-name=account-default-theme",
+    permission="change_settings",
+)
+def patch_change_account_default_theme(request: Request) -> Response:
+    """Change the user's "theme account default" setting."""
+    user = request.context
+
+    new_theme = request.params.get("theme")
+    user.theme_default = new_theme
+
+    return IC_NOOP
+
+
 @ic_view_config(
     route_name="user",
     request_method="PATCH",
@@ -288,7 +303,6 @@ def patch_change_user_bio(request: Request, markdown: str) -> dict:
 
     return IC_NOOP
 
-
 @ic_view_config(
     route_name="user",
     request_method="PATCH",
@@ -304,7 +318,6 @@ def patch_change_wpm(request: Request, words_per_minute: int) -> dict:
 
     return IC_NOOP
 
-
 @ic_view_config(
     route_name="user_invite_code",
     request_method="GET",