diff --git a/src/MongoDbEventStoreAdapter.php b/src/MongoDbEventStoreAdapter.php
index a4adc36..ff27257 100644
--- a/src/MongoDbEventStoreAdapter.php
+++ b/src/MongoDbEventStoreAdapter.php
@@ -157,7 +157,7 @@ public function appendTo(StreamName $streamName, Iterator $streamEvents)
         } catch (\MongoDB\Driver\Exception\BulkWriteException $e) {
             $code = isset($e->getWriteResult()->getWriteErrors()[0]) ?
                 $e->getWriteResult()->getWriteErrors()[0]->getCode()
-                : 0;
+                : $e->getCode();
 
             if (\in_array($code, [11000, 11001, 12582], true)) {
                 throw new ConcurrencyException('At least one event with same version exists already', 0, $e);
diff --git a/tests/MongoDbEventStoreAdapterTest.php b/tests/MongoDbEventStoreAdapterTest.php
index cf5b47d..58ec097 100644
--- a/tests/MongoDbEventStoreAdapterTest.php
+++ b/tests/MongoDbEventStoreAdapterTest.php
@@ -17,6 +17,7 @@
 use Prooph\Common\Messaging\NoOpMessageConverter;
 use Prooph\EventStore\Adapter\MongoDb\Exception\RuntimeAdapterException;
 use Prooph\EventStore\Adapter\MongoDb\MongoDbEventStoreAdapter;
+use Prooph\EventStore\Exception\ConcurrencyException;
 use Prooph\EventStore\Stream\Stream;
 use Prooph\EventStore\Stream\StreamName;
 use ProophTest\EventStore\Mock\UserCreated;
@@ -541,6 +542,37 @@ public function it_writes_to_different_streams_in_one_transaction_if_they_exists
         $this->assertEquals(2, $this->client->selectCollection($dbName, 'another_test_stream')->countDocuments());
     }
 
+    /**
+     * @test
+     */
+    public function it_throws_concurrency_exception_on_duplicate_key_error(): void
+    {
+        $dbName = TestUtil::getDatabaseName();
+
+        $this->adapter = new MongoDbEventStoreAdapter(
+            new FQCNMessageFactory(),
+            new NoOpMessageConverter(),
+            $this->client,
+            $dbName,
+            [
+                'Prooph\Model\User' => 'test_collection_name',
+            ]
+        );
+
+        $testStream = $this->getTestStream();
+
+        $this->adapter->beginTransaction();
+
+        $this->adapter->create($testStream);
+
+        $this->expectException(ConcurrencyException::class);
+        $this->expectExceptionMessage('At least one event');
+
+        $this->adapter->appendTo($testStream->streamName(), $testStream->streamEvents());
+
+        $this->adapter->commit();
+    }
+
     /**
      * @test
      */