diff --git a/services/nginx/app/routes/departmentSelfserveVehicleConditionsRoute.php b/services/nginx/app/routes/departmentSelfserveVehicleConditionsRoute.php
index d6efafe6..4c1e4935 100644
--- a/services/nginx/app/routes/departmentSelfserveVehicleConditionsRoute.php
+++ b/services/nginx/app/routes/departmentSelfserveVehicleConditionsRoute.php
@@ -131,7 +131,7 @@ class departmentSelfserveVehicleConditionsRoute
             $lane_id = (int)self::getParameter('lane_id');
             $reg = selfserve::standardize_registration((string)self::getParameter('reg'));
 
-            $lane = $this->assertLaneAccess($user, $lane_id, $has_global);
+            $lane = $this->assertLaneAccess($user, $lane_id);
             $customer_number = null;
             if (!$has_global && $has_own) {
                 $customer_number = $this->requireAuthenticatedCustomerNumber($user, 'list_department_selfserve_vehicle_conditions');
@@ -193,7 +193,7 @@ class departmentSelfserveVehicleConditionsRoute
                 $lane_id = (int)self::getParameter('lane_id');
                 $reg = selfserve::standardize_registration((string)self::getParameter('reg'));
 
-                $this->assertLaneAccess($user, $lane_id, $has_global);
+                $this->assertLaneAccess($user, $lane_id);
                 $customer_number = null;
                 if (!$has_global && $has_own) {
                     $customer_number = $this->requireAuthenticatedCustomerNumber($user, 'list_department_selfserve_vehicle_conditions');
@@ -527,7 +527,7 @@ class departmentSelfserveVehicleConditionsRoute
         return $default;
     }
 
-    private function assertLaneAccess(object $user, int $laneId, bool $hasGlobalPermission): department_lanes_o
+    private function assertLaneAccess(object $user, int $laneId): department_lanes_o
     {
         global $response;
 
@@ -536,11 +536,14 @@ class departmentSelfserveVehicleConditionsRoute
             $response->error('Department lane not found', 404);
         }
 
-        if ($hasGlobalPermission) {
-            $authorized_department_ids = $user->getGroup()->getDepartments();
-            if (!in_array((int)$lane->department->value(), $authorized_department_ids, true)) {
-                $this->forbidDepartmentAccess((int)$lane->department->value());
-            }
+        $lane_department_id = (int)$lane->department->value();
+        $authorized_department_ids = array_values(array_filter(
+            array_map('intval', (array)$user->getGroup()->getDepartments()),
+            static fn(int $department_id): bool => $department_id > 0
+        ));
+
+        if (!in_array($lane_department_id, $authorized_department_ids, true)) {
+            $this->forbidDepartmentAccess($lane_department_id);
         }
 
         return $lane;
diff --git a/services/nginx/app/tests/Unit/Selfserve/SelfserveEligibilityLaneAccessTest.php b/services/nginx/app/tests/Unit/Selfserve/SelfserveEligibilityLaneAccessTest.php
new file mode 100644
index 00000000..b9943bc8
--- /dev/null
+++ b/services/nginx/app/tests/Unit/Selfserve/SelfserveEligibilityLaneAccessTest.php
@@ -0,0 +1,58 @@
+<?php
+
+function selfserve_eligibility_route_source(): string
+{
+    $route = file_get_contents(app_path('routes/departmentSelfserveVehicleConditionsRoute.php'));
+    if ($route === false) {
+        throw new RuntimeException('departmentSelfserveVehicleConditionsRoute.php not found');
+    }
+
+    return $route;
+}
+
+function selfserve_eligibility_route_block(string $route, string $method, string $path): string
+{
+    $start = strpos($route, "\$this->{$method}('{$path}'");
+    if ($start === false) {
+        throw new RuntimeException("Route block not found: {$method} {$path}");
+    }
+
+    $nextComment = strpos($route, "\n        /**", $start + 1);
+    if ($nextComment === false) {
+        return substr($route, $start);
+    }
+
+    return substr($route, $start, $nextComment - $start);
+}
+
+function selfserve_eligibility_method_block(string $route, string $signature): string
+{
+    $start = strpos($route, $signature);
+    if ($start === false) {
+        throw new RuntimeException("Method not found: {$signature}");
+    }
+
+    $nextMethod = strpos($route, "\n    private function ", $start + strlen($signature));
+    if ($nextMethod === false) {
+        return substr($route, $start);
+    }
+
+    return substr($route, $start, $nextMethod - $start);
+}
+
+it('authorizes customer eligibility preview lanes before returning task attachments', function (): void {
+    $route = selfserve_eligibility_route_source();
+    $allowedBlock = selfserve_eligibility_route_block($route, 'get', '/department/selfserve/vehicle/allowed');
+    $assertBlock = selfserve_eligibility_method_block($route, 'private function assertLaneAccess(object $user, int $laneId): department_lanes_o');
+
+    expect($allowedBlock)->toContain('$lane = $this->assertLaneAccess($user, $lane_id);')
+        ->and($allowedBlock)->toContain('previewVehicleEligibility($lane_id, $reg, $customer_number, $vehicle_type_id)')
+        ->and(strpos($allowedBlock, '$lane = $this->assertLaneAccess($user, $lane_id);'))
+        ->toBeLessThan(strpos($allowedBlock, 'previewVehicleEligibility($lane_id, $reg, $customer_number, $vehicle_type_id)'));
+
+    expect($assertBlock)->toContain('$authorized_department_ids = array_values(array_filter(')
+        ->and($assertBlock)->toContain('array_map(\'intval\', (array)$user->getGroup()->getDepartments())')
+        ->and($assertBlock)->toContain('if (!in_array($lane_department_id, $authorized_department_ids, true))')
+        ->and($assertBlock)->toContain('$this->forbidDepartmentAccess($lane_department_id);')
+        ->and($assertBlock)->not->toContain('if ($hasGlobalPermission)');
+});