diff --git a/services/nginx/app/objects/order_bookings_o.php b/services/nginx/app/objects/order_bookings_o.php
index b5a15ec7..729378e2 100644
--- a/services/nginx/app/objects/order_bookings_o.php
+++ b/services/nginx/app/objects/order_bookings_o.php
@@ -354,16 +354,14 @@ class order_bookings_o extends db
     /**
      * @throws Exception
      */
-    public function completeBooking(int $user_id, string $safety_seal = null): void
+    public function completeBooking(int $user_id, ?string $safety_seal = null): void
     {
         self::requireSelected();
-        $orderWasCreatedDuringCompletion = false;
         if (!$this->order_id->value()) {
             // Create order, if not already created
             $this->createOrderBy($user_id);
             // Add order items, re-calculate the prices to be customer-specific
             $this->createOrderItemsBy($user_id);
-            $orderWasCreatedDuringCompletion = true;
         }
 
         if (!$this->containsWashCertificateItem()) {
@@ -377,12 +375,14 @@ class order_bookings_o extends db
             $order->objectChanged();
         }
 
-        if (!$orderWasCreatedDuringCompletion) {
+        if ($order->hasWashCertificateAttached()) {
             return;
         }
 
         $this->attachWashCertificate($user_id, $order->getSafetySealValue());
-        $this->sendWashCertificateToCustomer();
+        if ($order->hasWashCertificateAttached()) {
+            $this->sendWashCertificateToCustomer();
+        }
     }
 
     /**
@@ -465,7 +465,7 @@ class order_bookings_o extends db
     /**
      * @throws Exception
      */
-    protected function attachWashCertificate(int $user_id, string $safety_seal = null): void
+    protected function attachWashCertificate(int $user_id, ?string $safety_seal = null): void
     {
         self::requireSelected();
         // Check if the order already has a wash certificate attached
diff --git a/services/nginx/app/tests/Unit/Orders/OrderBookingsCompletionDedupTest.php b/services/nginx/app/tests/Unit/Orders/OrderBookingsCompletionDedupTest.php
index ececa258..810f6172 100644
--- a/services/nginx/app/tests/Unit/Orders/OrderBookingsCompletionDedupTest.php
+++ b/services/nginx/app/tests/Unit/Orders/OrderBookingsCompletionDedupTest.php
@@ -19,9 +19,16 @@ if (!class_exists('OrderBookingsCompletionOrderDouble')) {
             $this->completed_at = new object_property('orders', -1, 'completed_at', 'timestamp', false);
         }
 
+        public bool $washCertificateAttached = false;
+
         public function objectChanged(): void
         {
         }
+
+        public function hasWashCertificateAttached(): bool
+        {
+            return $this->washCertificateAttached;
+        }
     }
 }
 
@@ -65,9 +72,10 @@ if (!class_exists('OrderBookingsCompletionDouble')) {
             return $this->linkedOrder;
         }
 
-        protected function attachWashCertificate(int $user_id, string $safety_seal = null): void
+        protected function attachWashCertificate(int $user_id, ?string $safety_seal = null): void
         {
             $this->attachCalls++;
+            $this->linkedOrder->washCertificateAttached = true;
         }
 
         public function sendWashCertificateToCustomer(): void
@@ -77,7 +85,7 @@ if (!class_exists('OrderBookingsCompletionDouble')) {
     }
 }
 
-it('does not create or email a duplicate wash certificate when a booking is already linked to a pos order', function (): void {
+it('attaches and emails a wash certificate when a booking is already linked to a pos order without one', function (): void {
     $order = new OrderBookingsCompletionOrderDouble();
     $booking = new OrderBookingsCompletionDouble($order);
     $booking->order_id->set(321);
@@ -85,6 +93,20 @@ it('does not create or email a duplicate wash certificate when a booking is alre
 
     $booking->completeBooking(77, 'LINKED-SEAL');
 
+    expect($order->getSafetySealValue())->toBe('LINKED-SEAL');
+    expect($booking->attachCalls)->toBe(1);
+    expect($booking->sendCalls)->toBe(1);
+});
+
+it('does not create or email a duplicate wash certificate when a linked pos order already has one', function (): void {
+    $order = new OrderBookingsCompletionOrderDouble();
+    $order->washCertificateAttached = true;
+    $booking = new OrderBookingsCompletionDouble($order);
+    $booking->order_id->set(321);
+    $booking->containsWashCertificate = true;
+
+    $booking->completeBooking(77, 'LINKED-SEAL');
+
     expect($order->getSafetySealValue())->toBe('LINKED-SEAL');
     expect($booking->attachCalls)->toBe(0);
     expect($booking->sendCalls)->toBe(0);