diff --git a/k8s/charts/seaweedfs/templates/shared/security-configmap.yaml b/k8s/charts/seaweedfs/templates/shared/security-configmap.yaml
index a067e1de9..17b82cca0 100644
--- a/k8s/charts/seaweedfs/templates/shared/security-configmap.yaml
+++ b/k8s/charts/seaweedfs/templates/shared/security-configmap.yaml
@@ -97,6 +97,19 @@ data:
     cert = "/usr/local/share/ca-certificates/worker/tls.crt"
     key  = "/usr/local/share/ca-certificates/worker/tls.key"
 
+    {{- /* S3 gRPC server identity (weed s3 -port.grpc, default httpPort+10000).
+      Without this section, LoadServerTLS("grpc.s3") returns nil and the S3
+      server serves its internal gRPC (IAM cache propagation, s3 lifecycle
+      delete RPCs) as plaintext, while peers dial it with mTLS credentials:
+      "tls: first record does not look like a TLS handshake".
+      Always uses the internal CA-signed client certificate (already mounted
+      on s3 pods by s3-deployment.yaml). Deliberately NOT s3.tlsSecret: that
+      secret is for the public HTTPS listener and may be issued by a public
+      CA which internal gRPC peers (trusting only grpc.ca) would reject. */}}
+    [grpc.s3]
+    cert = "/usr/local/share/ca-certificates/client/tls.crt"
+    key  = "/usr/local/share/ca-certificates/client/tls.key"
+
     # use this for any place needs a grpc client
     # i.e., "weed backup|benchmark|filer.copy|filer.replicate|mount|s3|upload"
     [grpc.client]