diff --git a/lib/constructs/socket-mode.ts b/lib/constructs/socket-mode.ts
index ba59c0f..585d911 100644
--- a/lib/constructs/socket-mode.ts
+++ b/lib/constructs/socket-mode.ts
@@ -3,6 +3,7 @@ import * as cdk from 'aws-cdk-lib';
 import * as ec2 from 'aws-cdk-lib/aws-ec2';
 import * as ecs from 'aws-cdk-lib/aws-ecs';
 import * as ecr from 'aws-cdk-lib/aws-ecr';
+import * as ecrAssets from 'aws-cdk-lib/aws-ecr-assets';
 import * as logs from 'aws-cdk-lib/aws-logs';
 import * as iam from 'aws-cdk-lib/aws-iam';
 import * as dynamodb from 'aws-cdk-lib/aws-dynamodb';
@@ -76,6 +77,10 @@ export class SocketModeConstruct extends Construct {
     taskDef.addContainer('listener', {
       image: ecs.ContainerImage.fromAsset(
         path.join(__dirname, '../../listener'),
+        // Explicit platform: the task is ARM64, and without this an amd64 CI
+        // runner builds an amd64 image even with QEMU enabled — tasks then
+        // crash-loop with "exec format error" (50 failed starts on 2026-06-03).
+        { platform: ecrAssets.Platform.LINUX_ARM64 },
       ),
       essential: true,
       environment: {