diff --git a/api/src/routes/settings.test.ts b/api/src/routes/settings.test.ts
index 490bb9b3a93..4234aac421c 100644
--- a/api/src/routes/settings.test.ts
+++ b/api/src/routes/settings.test.ts
@@ -409,10 +409,10 @@ Please wait 5 minutes to resend an authentication link.`
           username: 'TwaHa1'
         });
 
-        expect(response.body).toEqual({
+        expect(response.body).toStrictEqual({
           message: 'flash.username-updated',
           type: 'success',
-          username: 'TwaHa1'
+          variables: { username: 'TwaHa1' }
         });
 
         const user = await fastifyTestInstance.prisma.user.findFirst({
@@ -470,10 +470,10 @@ Please wait 5 minutes to resend an authentication link.`
           username: 'TWaha3'
         });
 
-        expect(response.body).toEqual({
+        expect(response.body).toStrictEqual({
           message: 'flash.username-updated',
           type: 'success',
-          username: 'TWaha3'
+          variables: { username: 'TWaha3' }
         });
         expect(response.statusCode).toEqual(200);
       });
diff --git a/api/src/routes/settings.ts b/api/src/routes/settings.ts
index 81a07deaffc..c80f7f4eddb 100644
--- a/api/src/routes/settings.ts
+++ b/api/src/routes/settings.ts
@@ -358,11 +358,11 @@ ${isLinkSentWithinLimitTTL}`
 
         if (!validation.valid) {
           void reply.code(400);
-          return {
+          return reply.send({
             // TODO(Post-MVP): custom validation errors.
             message: `Username ${newUsername} ${validation.error}`,
             type: 'info'
-          } as const;
+          });
         }
 
         const isUserNameProfane = isProfane(newUsername);
@@ -377,10 +377,10 @@ ${isLinkSentWithinLimitTTL}`
 
         if (usernameTaken || isUserNameProfane || onBlocklist) {
           void reply.code(400);
-          return {
+          return reply.send({
             message: 'flash.username-taken',
             type: 'info'
-          } as const;
+          });
         }
 
         await fastify.prisma.user.update({
@@ -391,15 +391,15 @@ ${isLinkSentWithinLimitTTL}`
           }
         });
 
-        return {
+        return reply.send({
           message: 'flash.username-updated',
           type: 'success',
-          username: newUsernameDisplay
-        } as const;
+          variables: { username: newUsernameDisplay }
+        });
       } catch (err) {
         fastify.log.error(err);
         void reply.code(500);
-        return { message: 'flash.wrong-updating', type: 'danger' } as const;
+        await reply.send({ message: 'flash.wrong-updating', type: 'danger' });
       }
     }
   );
diff --git a/api/src/schemas/settings/update-my-username.ts b/api/src/schemas/settings/update-my-username.ts
index f7f04779eca..46df9b368ae 100644
--- a/api/src/schemas/settings/update-my-username.ts
+++ b/api/src/schemas/settings/update-my-username.ts
@@ -8,7 +8,7 @@ export const updateMyUsername = {
     200: Type.Object({
       message: Type.String(),
       type: Type.Literal('success'),
-      username: Type.String()
+      variables: Type.Object({ username: Type.String() })
     }),
     400: Type.Object({
       message: Type.Optional(Type.String()),