diff --git a/deploy/helm/openshell/templates/_helpers.tpl b/deploy/helm/openshell/templates/_helpers.tpl
index 3d9f2f3e0b..4a018ba941 100644
--- a/deploy/helm/openshell/templates/_helpers.tpl
+++ b/deploy/helm/openshell/templates/_helpers.tpl
@@ -274,6 +274,36 @@ Validate chart values that Helm would otherwise accept silently.
 {{- if and (eq $workloadKind "statefulset") (gt $replicaCount 1) (not (get $workload "allowMultiReplicaStatefulSet" | default false)) -}}
 {{- fail "replicaCount > 1 with workload.kind=statefulset requires workload.allowMultiReplicaStatefulSet=true; use workload.kind=deployment for external database-backed multi-replica gateways." -}}
 {{- end -}}
+{{- $servicePortValue := toString .Values.service.port -}}
+{{- $healthPortValue := toString .Values.service.healthPort -}}
+{{- $metricsPortValue := toString (default 0 .Values.service.metricsPort) -}}
+{{- if not (regexMatch `^-?[0-9]+$` $servicePortValue) -}}
+{{- fail "service.port must be an integer." -}}
+{{- end -}}
+{{- if not (regexMatch `^-?[0-9]+$` $healthPortValue) -}}
+{{- fail "service.healthPort must be an integer." -}}
+{{- end -}}
+{{- if not (regexMatch `^-?[0-9]+$` $metricsPortValue) -}}
+{{- fail "service.metricsPort must be an integer." -}}
+{{- end -}}
+{{- $servicePort := int $servicePortValue -}}
+{{- $healthPort := int $healthPortValue -}}
+{{- $metricsPort := int $metricsPortValue -}}
+{{- if or (lt $servicePort 1) (gt $servicePort 65535) -}}
+{{- fail "service.port must be between 1 and 65535." -}}
+{{- end -}}
+{{- if or (lt $healthPort 1) (gt $healthPort 65535) -}}
+{{- fail "service.healthPort must be between 1 and 65535 because gateway probes require it." -}}
+{{- end -}}
+{{- if eq $servicePort $healthPort -}}
+{{- fail "service.port and service.healthPort must be different." -}}
+{{- end -}}
+{{- if and (ne $metricsPort 0) (or (lt $metricsPort 1) (gt $metricsPort 65535)) -}}
+{{- fail "service.metricsPort must be 0 (disabled) or between 1 and 65535." -}}
+{{- end -}}
+{{- if and (ne $metricsPort 0) (or (eq $metricsPort $servicePort) (eq $metricsPort $healthPort)) -}}
+{{- fail "service.metricsPort must differ from service.port and service.healthPort." -}}
+{{- end -}}
 {{- $workspaceMode := .Values.server.drivers.kubernetes.workspaceMode | default "shared" -}}
 {{- if not (has $workspaceMode (list "shared" "managed" "operator")) -}}
 {{- fail "server.drivers.kubernetes.workspaceMode must be one of: shared, managed, operator." -}}
diff --git a/deploy/helm/openshell/tests/gateway_ports_test.yaml b/deploy/helm/openshell/tests/gateway_ports_test.yaml
new file mode 100644
index 0000000000..6aa4e76346
--- /dev/null
+++ b/deploy/helm/openshell/tests/gateway_ports_test.yaml
@@ -0,0 +1,129 @@
+# SPDX-FileCopyrightText: Copyright (c) 2025-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+
+suite: gateway listener port validation
+templates:
+  - templates/gateway-config.yaml
+  - templates/statefulset.yaml
+
+tests:
+  - it: rejects primary gateway port 0
+    template: templates/statefulset.yaml
+    set:
+      service.port: 0
+    asserts:
+      - failedTemplate:
+          errorPattern: "service.port must be between 1 and 65535"
+
+  - it: rejects a primary gateway listener above the valid port range
+    template: templates/statefulset.yaml
+    set:
+      service.port: 65536
+    asserts:
+      - failedTemplate:
+          errorPattern: "service.port must be between 1 and 65535"
+
+  - it: rejects a disabled health listener because probes require it
+    template: templates/statefulset.yaml
+    set:
+      service.healthPort: 0
+    asserts:
+      - failedTemplate:
+          errorPattern: "service.healthPort must be between 1 and 65535 because gateway probes require it"
+
+  - it: rejects a health listener above the valid port range
+    template: templates/statefulset.yaml
+    set:
+      service.healthPort: 65536
+    asserts:
+      - failedTemplate:
+          errorPattern: "service.healthPort must be between 1 and 65535 because gateway probes require it"
+
+  - it: rejects a health listener that collides with the primary listener
+    template: templates/statefulset.yaml
+    set:
+      service.healthPort: 8080
+    asserts:
+      - failedTemplate:
+          errorPattern: "service.port and service.healthPort must be different"
+
+  - it: rejects a metrics listener that collides with the primary listener
+    template: templates/statefulset.yaml
+    set:
+      service.metricsPort: 8080
+    asserts:
+      - failedTemplate:
+          errorPattern: "service.metricsPort must differ from service.port and service.healthPort"
+
+  - it: rejects a metrics listener that collides with the health listener
+    template: templates/statefulset.yaml
+    set:
+      service.metricsPort: 8081
+    asserts:
+      - failedTemplate:
+          errorPattern: "service.metricsPort must differ from service.port and service.healthPort"
+
+  - it: rejects a negative metrics listener port
+    template: templates/statefulset.yaml
+    set:
+      service.metricsPort: -1
+    asserts:
+      - failedTemplate:
+          errorPattern: "service.metricsPort must be 0 \\(disabled\\) or between 1 and 65535"
+
+  - it: rejects a boolean primary port
+    template: templates/statefulset.yaml
+    set:
+      service.port: true
+    asserts:
+      - failedTemplate:
+          errorPattern: "service.port must be an integer"
+
+  - it: rejects a boolean health port
+    template: templates/statefulset.yaml
+    set:
+      service.healthPort: true
+    asserts:
+      - failedTemplate:
+          errorPattern: "service.healthPort must be an integer"
+
+  - it: rejects a boolean metrics port
+    template: templates/statefulset.yaml
+    set:
+      service.metricsPort: true
+    asserts:
+      - failedTemplate:
+          errorPattern: "service.metricsPort must be an integer"
+
+  - it: rejects a fractional metrics port
+    template: templates/statefulset.yaml
+    set:
+      service.metricsPort: 9090.5
+    asserts:
+      - failedTemplate:
+          errorPattern: "service.metricsPort must be an integer"
+
+  - it: rejects a metrics listener above the valid port range
+    template: templates/statefulset.yaml
+    set:
+      service.metricsPort: 65536
+    asserts:
+      - failedTemplate:
+          errorPattern: "service.metricsPort must be 0 \\(disabled\\) or between 1 and 65535"
+
+  - it: accepts boundary ports with metrics disabled
+    template: templates/gateway-config.yaml
+    set:
+      service.port: 1
+      service.healthPort: 65535
+      service.metricsPort: 0
+    asserts:
+      - matchRegex:
+          path: data["gateway.toml"]
+          pattern: '(?m)^bind_address\s*=\s*"0\.0\.0\.0:1"$'
+      - matchRegex:
+          path: data["gateway.toml"]
+          pattern: '(?m)^health_bind_address\s*=\s*"0\.0\.0\.0:65535"$'
+      - notMatchRegex:
+          path: data["gateway.toml"]
+          pattern: '(?m)^metrics_bind_address\s*='