diff --git a/ModelDescriber/Annotations/SymfonyConstraintAnnotationReader.php b/ModelDescriber/Annotations/SymfonyConstraintAnnotationReader.php
index ccd9cb0..af1ade0 100644
--- a/ModelDescriber/Annotations/SymfonyConstraintAnnotationReader.php
+++ b/ModelDescriber/Annotations/SymfonyConstraintAnnotationReader.php
@@ -48,6 +48,11 @@ class SymfonyConstraintAnnotationReader
 
         foreach ($annotations as $annotation) {
             if ($annotation instanceof Assert\NotBlank || $annotation instanceof Assert\NotNull) {
+                if ($annotation instanceof Assert\NotBlank && $annotation->allowNull) {
+                    // The field is optional
+                    continue;
+                }
+
                 // The field is required
                 if (null === $this->schema) {
                     continue;
diff --git a/Tests/ModelDescriber/Annotations/SymfonyConstraintAnnotationReaderTest.php b/Tests/ModelDescriber/Annotations/SymfonyConstraintAnnotationReaderTest.php
index 42f6e96..f6a3c1c 100644
--- a/Tests/ModelDescriber/Annotations/SymfonyConstraintAnnotationReaderTest.php
+++ b/Tests/ModelDescriber/Annotations/SymfonyConstraintAnnotationReaderTest.php
@@ -47,6 +47,34 @@ class SymfonyConstraintAnnotationReaderTest extends TestCase
         $this->assertEquals($schema->required, ['property1', 'property2']);
     }
 
+    public function testOptionalProperty()
+    {
+        $entity = new class() {
+            /**
+             * @Assert\NotBlank(allowNull = true)
+             * @Assert\Length(min = 1)
+             */
+            private $property1;
+            /**
+             * @Assert\NotBlank()
+             */
+            private $property2;
+        };
+
+        $schema = new Schema();
+        $schema->getProperties()->set('property1', new Schema());
+        $schema->getProperties()->set('property2', new Schema());
+
+        $symfonyConstraintAnnotationReader = new SymfonyConstraintAnnotationReader(new AnnotationReader());
+        $symfonyConstraintAnnotationReader->setSchema($schema);
+
+        $symfonyConstraintAnnotationReader->updateProperty(new \ReflectionProperty($entity, 'property1'), $schema->getProperties()->get('property1'));
+        $symfonyConstraintAnnotationReader->updateProperty(new \ReflectionProperty($entity, 'property2'), $schema->getProperties()->get('property2'));
+
+        // expect required to be numeric array with sequential keys (not [0 => ..., 2 => ...])
+        $this->assertEquals($schema->getRequired(), ['property2']);
+    }
+
     public function testAssertChoiceResultsInNumericArray()
     {
         define('TEST_ASSERT_CHOICE_STATUSES', [