diff --git a/keyserver/src/responders/thread-responders.js b/keyserver/src/responders/thread-responders.js
--- a/keyserver/src/responders/thread-responders.js
+++ b/keyserver/src/responders/thread-responders.js
@@ -19,6 +19,7 @@
   type ThreadFetchMediaRequest,
   threadTypes,
 } from 'lib/types/thread-types.js';
+import { updateUserAvatarRequestValidator } from 'lib/utils/avatar-utils.js';
 import { values } from 'lib/utils/objects.js';
 import {
   tShape,
@@ -112,6 +113,7 @@
     color: t.maybe(tColor),
     parentThreadID: t.maybe(t.String),
     newMemberIDs: t.maybe(t.list(t.String)),
+    avatar: t.maybe(updateUserAvatarRequestValidator),
   }),
   accountPassword: t.maybe(tPassword),
 });
diff --git a/keyserver/src/updaters/thread-updaters.js b/keyserver/src/updaters/thread-updaters.js
--- a/keyserver/src/updaters/thread-updaters.js
+++ b/keyserver/src/updaters/thread-updaters.js
@@ -356,6 +356,13 @@
     sqlUpdate.parent_thread_id = parentThreadID;
   }
 
+  const { avatar } = request.changes;
+  if (avatar) {
+    changedFields.avatar =
+      avatar.type !== 'remove' ? JSON.stringify(avatar) : '';
+    sqlUpdate.avatar = avatar.type !== 'remove' ? JSON.stringify(avatar) : null;
+  }
+
   const threadType = request.changes.type;
   if (threadType !== null && threadType !== undefined) {
     changedFields.type = threadType;
@@ -412,6 +419,12 @@
         permission: threadPermissions.EDIT_THREAD_COLOR,
       });
     }
+    if (sqlUpdate.avatar !== undefined) {
+      checks.push({
+        check: 'permission',
+        permission: threadPermissions.EDIT_THREAD_AVATAR,
+      });
+    }
     if (parentThreadID !== undefined || sqlUpdate.type !== undefined) {
       checks.push({
         check: 'permission',
diff --git a/lib/types/thread-types.js b/lib/types/thread-types.js
--- a/lib/types/thread-types.js
+++ b/lib/types/thread-types.js
@@ -2,7 +2,7 @@
 
 import invariant from 'invariant';
 
-import type { ClientAvatar } from './avatar-types.js';
+import type { ClientAvatar, UpdateUserAvatarRequest } from './avatar-types.js';
 import type { Shape } from './core.js';
 import type { CalendarQuery, RawEntryInfo } from './entry-types.js';
 import type { Media } from './media-types.js';
@@ -384,6 +384,7 @@
   +color: string,
   +parentThreadID: ?string,
   +newMemberIDs: $ReadOnlyArray<string>,
+  +avatar: UpdateUserAvatarRequest,
 }>;
 
 export type UpdateThreadRequest = {