diff --git a/app/Models/Customer.php b/app/Models/Customer.php
index 56cee53..2687655 100644
--- a/app/Models/Customer.php
+++ b/app/Models/Customer.php
@@ -8,10 +8,8 @@ use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\Relations\BelongsTo;
 use Illuminate\Database\Eloquent\Relations\HasMany;
 use Illuminate\Database\UniqueConstraintViolationException;
-use Illuminate\Support\Facades\Auth;
 use Illuminate\Support\Facades\Hash;
 use Illuminate\Support\Str;
-use RuntimeException;
 
 class Customer extends Model
 {
@@ -99,9 +97,10 @@ class Customer extends Model
 
     /**
      * Find or create the portal login account for this customer and link it.
-     * Race-safe against the unique email index, and never links an operator
-     * account — that would carry admin authorization into an impersonated
-     * "customer" session.
+     * Race-safe against the unique email index. Never links an operator
+     * account by construction, not by a runtime check: operators live in
+     * `operators`, on their own guard, and are never rows in `users` at all
+     * (see R21) — there is no longer an admin `users` row this could find.
      */
     public function ensureUser(): User
     {
@@ -110,7 +109,6 @@ class Customer extends Model
         }
 
         if (($existing = User::query()->where('email', $this->email)->first()) !== null) {
-            $this->assertNotAdmin($existing);
             $this->update(['user_id' => $existing->id]);
 
             return $existing;
@@ -121,25 +119,14 @@ class Customer extends Model
                 'email' => $this->email,
                 'name' => $this->name,
                 'password' => Hash::make(Str::random(40)),
-                'is_admin' => false,
             ]);
         } catch (UniqueConstraintViolationException) {
             // Concurrent first-time creation — re-fetch and link the winner.
             $user = User::query()->where('email', $this->email)->firstOrFail();
-            $this->assertNotAdmin($user);
         }
 
         $this->update(['user_id' => $user->id]);
 
         return $user->refresh();
     }
-
-    private function assertNotAdmin(User $user): void
-    {
-        if (Auth::guard('operator')->check()) {
-            throw new RuntimeException(
-                "Refusing to link operator account {$user->email} as a portal login for customer {$this->id}.",
-            );
-        }
-    }
 }
diff --git a/tests/Feature/ImpersonationTest.php b/tests/Feature/ImpersonationTest.php
index decc340..325b5ee 100644
--- a/tests/Feature/ImpersonationTest.php
+++ b/tests/Feature/ImpersonationTest.php
@@ -2,6 +2,7 @@
 
 use App\Models\Customer;
 use App\Models\Operator;
+use App\Models\User;
 use Illuminate\Support\Facades\Auth;
 use Illuminate\Support\Facades\URL;
 
@@ -17,6 +18,36 @@ it('hands over a signed link instead of relying on a shared cookie', function ()
     $response->assertRedirectContains('signature=');
 });
 
+it('impersonates a customer who already has a portal login, with the operator session still active throughout', function () {
+    // Customer::assertNotAdmin() used to check Auth::guard('operator')->check()
+    // instead of inspecting the `users` row it was actually handed — so with
+    // the OPERATOR's own session still attached (same host, non-exclusive/
+    // shared mode — exactly the setup start() -> enter() runs under here,
+    // same test client, same cookies throughout, precisely how a real
+    // operator's browser carries its session across both legs in shared
+    // mode), ensureUser() threw the instant it found a `users` row that
+    // already existed for the customer's email: a 500 on the very first
+    // impersonation of anyone who had ever signed into the portal
+    // themselves. The guard is gone now (I5) — this is what "gone" has to
+    // mean in practice.
+    $operator = Operator::factory()->role('Owner')->create();
+    $customer = Customer::factory()->create();
+
+    // A portal login that exists independently of any impersonation — e.g.
+    // the customer signed up themselves before ever being impersonated.
+    User::factory()->create(['email' => $customer->email]);
+
+    $response = $this->actingAs($operator, 'operator')
+        ->post(route('admin.impersonate', $customer));
+
+    $location = $response->headers->get('Location');
+
+    $this->get($location)->assertRedirect(route('dashboard'));
+
+    expect(Auth::guard('web')->check())->toBeTrue()
+        ->and(Auth::guard('web')->user()->email)->toBe($customer->email);
+});
+
 it('signs the customer in on the web guard when the link is followed', function () {
     $operator = Operator::factory()->role('Owner')->create();
     $customer = Customer::factory()->create();