diff --git a/modules/openapi-generator/src/main/resources/php-nextgen/model_generic.mustache b/modules/openapi-generator/src/main/resources/php-nextgen/model_generic.mustache
index f79f5190888..c81f28e4190 100644
--- a/modules/openapi-generator/src/main/resources/php-nextgen/model_generic.mustache
+++ b/modules/openapi-generator/src/main/resources/php-nextgen/model_generic.mustache
@@ -190,6 +190,12 @@ class {{classname}} {{#parentSchema}}extends {{{parent}}}{{/parentSchema}}{{^par
         return self::$openAPIModelName;
     }
 
+{{#discriminator}}
+{{#discriminator.mappedModels}}
+    public const {{#lambda.uppercase}}{{discriminator.propertyName}}_{{#lambda.snakecase}}{{mappingName}}{{/lambda.snakecase}}{{/lambda.uppercase}} = '{{mappingName}}';
+{{/discriminator.mappedModels}}
+{{/discriminator}}
+{{^discriminator}}
     {{#vars}}
     {{#isEnum}}
     {{#allowableValues}}
@@ -199,6 +205,7 @@ class {{classname}} {{#parentSchema}}extends {{{parent}}}{{/parentSchema}}{{^par
     {{/allowableValues}}
     {{/isEnum}}
     {{/vars}}
+{{/discriminator}}
 
     {{#vars}}
     {{#isEnum}}
@@ -210,8 +217,15 @@ class {{classname}} {{#parentSchema}}extends {{{parent}}}{{/parentSchema}}{{^par
     public function {{getter}}AllowableValues()
     {
         return [
+{{#discriminator}}
+{{#discriminator.mappedModels}}
+            self::{{#lambda.uppercase}}{{discriminator.propertyName}}_{{#lambda.snakecase}}{{mappingName}}{{/lambda.snakecase}}{{/lambda.uppercase}},{{^-last}}
+{{/-last}}{{/discriminator.mappedModels}}
+{{/discriminator}}
+{{^discriminator}}
             {{#allowableValues}}{{#enumVars}}self::{{enumName}}_{{{name}}},{{^-last}}
             {{/-last}}{{/enumVars}}{{/allowableValues}}
+{{/discriminator}}
         ];
     }
 
@@ -233,6 +247,11 @@ class {{classname}} {{#parentSchema}}extends {{{parent}}}{{/parentSchema}}{{^par
      */
     public function __construct(array $data = null)
     {
+        {{#discriminator}}
+        // Initialize discriminator property with the model name.
+        $this->container['{{discriminatorName}}'] = static::$openAPIModelName;
+
+        {{/discriminator}}
         {{#parentSchema}}
         parent::__construct($data);
 
@@ -240,11 +259,6 @@ class {{classname}} {{#parentSchema}}extends {{{parent}}}{{/parentSchema}}{{^par
         {{#vars}}
         $this->setIfExists('{{name}}', $data ?? [], {{#defaultValue}}{{{defaultValue}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}});
         {{/vars}}
-        {{#discriminator}}
-
-        // Initialize discriminator property with the model name.
-        $this->container['{{discriminatorName}}'] = static::$openAPIModelName;
-        {{/discriminator}}
     }
 
     /**
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Animal.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Animal.php
index 3d9221bf721..ff8d05b36e6 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Animal.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Animal.php
@@ -233,6 +233,8 @@ class Animal implements ModelInterface, ArrayAccess, JsonSerializable
         return self::$openAPIModelName;
     }
 
+    public const CLASS_NAME_CAT = 'CAT';
+    public const CLASS_NAME_DOG = 'DOG';
 
     /**
      * Associative array for storing property values
@@ -248,11 +250,11 @@ class Animal implements ModelInterface, ArrayAccess, JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->setIfExists('class_name', $data ?? [], null);
-        $this->setIfExists('color', $data ?? [], 'red');
-
         // Initialize discriminator property with the model name.
         $this->container['class_name'] = static::$openAPIModelName;
+
+        $this->setIfExists('class_name', $data ?? [], null);
+        $this->setIfExists('color', $data ?? [], 'red');
     }
 
     /**
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ParentWithNullable.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ParentWithNullable.php
index 21bb921932d..bab081d0f9e 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ParentWithNullable.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ParentWithNullable.php
@@ -261,11 +261,11 @@ class ParentWithNullable implements ModelInterface, ArrayAccess, JsonSerializabl
      */
     public function __construct(array $data = null)
     {
-        $this->setIfExists('type', $data ?? [], null);
-        $this->setIfExists('nullable_property', $data ?? [], null);
-
         // Initialize discriminator property with the model name.
         $this->container['type'] = static::$openAPIModelName;
+
+        $this->setIfExists('type', $data ?? [], null);
+        $this->setIfExists('nullable_property', $data ?? [], null);
     }
 
     /**