diff --git a/lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php b/lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php
index 7794c8c4d..0747d4435 100644
--- a/lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php
+++ b/lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php
@@ -3003,7 +3003,7 @@ class ClassMetadataInfo implements ClassMetadata
      */
     public function setSequenceGeneratorDefinition(array $definition)
     {
-        if ( ! isset($definition['sequenceName'])) {
+        if ( ! isset($definition['sequenceName']) || trim($definition['sequenceName']) === '') {
             throw MappingException::missingSequenceName($this->name);
         }
 
@@ -3012,6 +3012,14 @@ class ClassMetadataInfo implements ClassMetadata
             $definition['quoted'] = true;
         }
 
+        if ( ! isset($definition['allocationSize']) || trim($definition['allocationSize']) === '') {
+            $definition['allocationSize'] = '1';
+        }
+
+        if ( ! isset($definition['initialValue']) || trim($definition['initialValue']) === '') {
+            $definition['initialValue'] = '1';
+        }
+
         $this->sequenceGeneratorDefinition = $definition;
     }
 
diff --git a/tests/Doctrine/Tests/ORM/Functional/Ticket/GH6682Test.php b/tests/Doctrine/Tests/ORM/Functional/Ticket/GH6682Test.php
new file mode 100644
index 000000000..a8fd76fa2
--- /dev/null
+++ b/tests/Doctrine/Tests/ORM/Functional/Ticket/GH6682Test.php
@@ -0,0 +1,29 @@
+<?php
+
+namespace Doctrine\Test\ORM\Functional\Ticket;
+
+use Doctrine\ORM\Mapping\ClassMetadataInfo;
+use Doctrine\Tests\OrmFunctionalTestCase;
+
+final class GH6682Test extends OrmFunctionalTestCase
+{
+    /**
+     * @group 6682
+     */
+    public function testIssue() : void
+    {
+        $parsedDefinition = [
+            'sequenceName'   => 'test_sequence',
+            'allocationSize' => '',
+            'initialValue'   => '',
+        ];
+
+        $classMetadataInfo = new ClassMetadataInfo('test_entity');
+        $classMetadataInfo->setSequenceGeneratorDefinition($parsedDefinition);
+
+        self::assertSame(
+            ['sequenceName' => 'test_sequence', 'allocationSize' => '1', 'initialValue' => '1'],
+            $classMetadataInfo->sequenceGeneratorDefinition
+        );
+    }
+}
diff --git a/tests/Doctrine/Tests/ORM/Mapping/ClassMetadataTest.php b/tests/Doctrine/Tests/ORM/Mapping/ClassMetadataTest.php
index 24d9559f7..a7be70be8 100644
--- a/tests/Doctrine/Tests/ORM/Mapping/ClassMetadataTest.php
+++ b/tests/Doctrine/Tests/ORM/Mapping/ClassMetadataTest.php
@@ -1188,15 +1188,19 @@ class ClassMetadataTest extends OrmTestCase
 
     /**
      * @group DDC-2662
+     * @group 6682
      */
-    public function testQuotedSequenceName()
+    public function testQuotedSequenceName() : void
     {
         $cm = new ClassMetadata(CMS\CmsUser::class);
-        $cm->initializeReflection(new RuntimeReflectionService());
 
+        $cm->initializeReflection(new RuntimeReflectionService());
         $cm->setSequenceGeneratorDefinition(['sequenceName' => '`foo`']);
 
-        $this->assertEquals(['sequenceName' => 'foo', 'quoted' => true], $cm->sequenceGeneratorDefinition);
+        self::assertSame(
+            ['sequenceName' => 'foo', 'quoted' => true, 'allocationSize' => '1', 'initialValue' => '1'],
+            $cm->sequenceGeneratorDefinition
+        );
     }
 
     /**