diff --git a/modules/openapi-generator/src/main/resources/php/ObjectSerializer.mustache b/modules/openapi-generator/src/main/resources/php/ObjectSerializer.mustache
index f5f0e5119ef..99b992ed5dd 100644
--- a/modules/openapi-generator/src/main/resources/php/ObjectSerializer.mustache
+++ b/modules/openapi-generator/src/main/resources/php/ObjectSerializer.mustache
@@ -31,6 +31,19 @@ use {{modelPackage}}\ModelInterface;
  */
 class ObjectSerializer
 {
+    /** @var string */
+    private static $dateTimeFormat = \DateTime::ATOM;
+
+    /**
+     * Change the date format
+     *
+     * @param string $format   the new date format to use
+     */
+    public static function setDateTimeFormat($format)
+    {
+        self::$dateTimeFormat = $format;
+    }
+
     /**
      * Serialize data
      *
@@ -45,7 +58,7 @@ class ObjectSerializer
         if (is_scalar($data) || null === $data) {
             return $data;
         } elseif ($data instanceof \DateTime) {
-            return ($format === 'date') ? $data->format('Y-m-d') : $data->format(\DateTime::ATOM);
+            return ($format === 'date') ? $data->format('Y-m-d') : $data->format(self::$dateTimeFormat);
         } elseif (is_array($data)) {
             foreach ($data as $property => $value) {
                 $data[$property] = self::sanitizeForSerialization($value);
@@ -178,7 +191,7 @@ class ObjectSerializer
     public static function toString($value)
     {
         if ($value instanceof \DateTime) { // datetime in ISO8601 format
-            return $value->format(\DateTime::ATOM);
+            return $value->format(self::$dateTimeFormat);
         } else if (is_bool($value)) {
             return $value ? 'true' : 'false';
         } else {
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php b/samples/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php
index cdae80a4e82..3569ce8ce4c 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php
@@ -41,6 +41,19 @@ use OpenAPI\Client\Model\ModelInterface;
  */
 class ObjectSerializer
 {
+    /** @var string */
+    private static $dateTimeFormat = \DateTime::ATOM;
+
+    /**
+     * Change the date format
+     *
+     * @param string $format   the new date format to use
+     */
+    public static function setDateTimeFormat($format)
+    {
+        self::$dateTimeFormat = $format;
+    }
+
     /**
      * Serialize data
      *
@@ -55,7 +68,7 @@ class ObjectSerializer
         if (is_scalar($data) || null === $data) {
             return $data;
         } elseif ($data instanceof \DateTime) {
-            return ($format === 'date') ? $data->format('Y-m-d') : $data->format(\DateTime::ATOM);
+            return ($format === 'date') ? $data->format('Y-m-d') : $data->format(self::$dateTimeFormat);
         } elseif (is_array($data)) {
             foreach ($data as $property => $value) {
                 $data[$property] = self::sanitizeForSerialization($value);
@@ -188,7 +201,7 @@ class ObjectSerializer
     public static function toString($value)
     {
         if ($value instanceof \DateTime) { // datetime in ISO8601 format
-            return $value->format(\DateTime::ATOM);
+            return $value->format(self::$dateTimeFormat);
         } else if (is_bool($value)) {
             return $value ? 'true' : 'false';
         } else {
diff --git a/samples/client/petstore/php/OpenAPIClient-php/tests/DateTimeSerializerTest.php b/samples/client/petstore/php/OpenAPIClient-php/tests/DateTimeSerializerTest.php
index 3a889cba6da..ca0fc505d6d 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/tests/DateTimeSerializerTest.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/tests/DateTimeSerializerTest.php
@@ -18,6 +18,11 @@ class DateTimeSerializerTest extends TestCase
         $data = ObjectSerializer::sanitizeForSerialization($input);
 
         $this->assertEquals($data->dateTime, '1973-04-30T17:05:00+02:00');
+
+        ObjectSerializer::setDateTimeFormat(\DateTime::RFC3339_EXTENDED);
+        $dataFraction = ObjectSerializer::sanitizeForSerialization($input);
+        $this->assertEquals($dataFraction->dateTime, '1973-04-30T17:05:00.000+02:00');
+        ObjectSerializer::setDateTimeFormat(\DateTime::ATOM);
     }
 
     public function testDateSanitazion()
diff --git a/samples/openapi3/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php b/samples/openapi3/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php
index cdae80a4e82..3569ce8ce4c 100644
--- a/samples/openapi3/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php
+++ b/samples/openapi3/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php
@@ -41,6 +41,19 @@ use OpenAPI\Client\Model\ModelInterface;
  */
 class ObjectSerializer
 {
+    /** @var string */
+    private static $dateTimeFormat = \DateTime::ATOM;
+
+    /**
+     * Change the date format
+     *
+     * @param string $format   the new date format to use
+     */
+    public static function setDateTimeFormat($format)
+    {
+        self::$dateTimeFormat = $format;
+    }
+
     /**
      * Serialize data
      *
@@ -55,7 +68,7 @@ class ObjectSerializer
         if (is_scalar($data) || null === $data) {
             return $data;
         } elseif ($data instanceof \DateTime) {
-            return ($format === 'date') ? $data->format('Y-m-d') : $data->format(\DateTime::ATOM);
+            return ($format === 'date') ? $data->format('Y-m-d') : $data->format(self::$dateTimeFormat);
         } elseif (is_array($data)) {
             foreach ($data as $property => $value) {
                 $data[$property] = self::sanitizeForSerialization($value);
@@ -188,7 +201,7 @@ class ObjectSerializer
     public static function toString($value)
     {
         if ($value instanceof \DateTime) { // datetime in ISO8601 format
-            return $value->format(\DateTime::ATOM);
+            return $value->format(self::$dateTimeFormat);
         } else if (is_bool($value)) {
             return $value ? 'true' : 'false';
         } else {
diff --git a/samples/openapi3/client/petstore/php/OpenAPIClient-php/tests/DateTimeSerializerTest.php b/samples/openapi3/client/petstore/php/OpenAPIClient-php/tests/DateTimeSerializerTest.php
index 3a889cba6da..ca0fc505d6d 100644
--- a/samples/openapi3/client/petstore/php/OpenAPIClient-php/tests/DateTimeSerializerTest.php
+++ b/samples/openapi3/client/petstore/php/OpenAPIClient-php/tests/DateTimeSerializerTest.php
@@ -18,6 +18,11 @@ class DateTimeSerializerTest extends TestCase
         $data = ObjectSerializer::sanitizeForSerialization($input);
 
         $this->assertEquals($data->dateTime, '1973-04-30T17:05:00+02:00');
+
+        ObjectSerializer::setDateTimeFormat(\DateTime::RFC3339_EXTENDED);
+        $dataFraction = ObjectSerializer::sanitizeForSerialization($input);
+        $this->assertEquals($dataFraction->dateTime, '1973-04-30T17:05:00.000+02:00');
+        ObjectSerializer::setDateTimeFormat(\DateTime::ATOM);
     }
 
     public function testDateSanitazion()