diff --git a/app/RandomOrderConfirmationNumberGenerator.php b/app/RandomOrderConfirmationNumberGenerator.php
index 5410632..a9e2719 100644
--- a/app/RandomOrderConfirmationNumberGenerator.php
+++ b/app/RandomOrderConfirmationNumberGenerator.php
@@ -6,6 +6,8 @@ class RandomOrderConfirmationNumberGenerator implements OrderConfirmationNumberG
 {
     public function generate()
     {
-        return str_repeat('A', 24);
+        $pool = 'ABCDEFGHJKLMNPQRSTUVWXYZ23456789';
+
+        return substr(str_shuffle(str_repeat($pool, 24)), 0, 24);
     }
 }
diff --git a/tests/unit/RandomOrderConfirmationNumberGeneratorTest.php b/tests/unit/RandomOrderConfirmationNumberGeneratorTest.php
index ac0d79e..3e9065a 100644
--- a/tests/unit/RandomOrderConfirmationNumberGeneratorTest.php
+++ b/tests/unit/RandomOrderConfirmationNumberGeneratorTest.php
@@ -47,4 +47,16 @@ class RandomOrderConfirmationNumberGeneratorTest extends TestCase
         $this->assertFalse(strpos($confirmationNumber, '0'));
         $this->assertFalse(strpos($confirmationNumber, 'O'));
     }
+
+    /** @test */
+    function confirmation_numbers_must_be_unique()
+    {
+        $generator = new RandomOrderConfirmationNumberGenerator;
+
+        $confirmationNumbers = array_map(function ($i) use ($generator) {
+            return $generator->generate();
+        }, range(1, 100));
+
+        $this->assertCount(100, array_unique($confirmationNumbers));
+    }
 }