diff --git a/admin-dev/themes/default/template/products/informations.tpl b/admin-dev/themes/default/template/products/informations.tpl
index 709e04a1d..19139f0c5 100644
--- a/admin-dev/themes/default/template/products/informations.tpl
+++ b/admin-dev/themes/default/template/products/informations.tpl
@@ -67,15 +67,15 @@
 	<div>
 		<label>{l s='Type:'}</label>
 		<label style="font-weight:normal;width:100px;text-align:center;">
-			<input type="radio" name="type_product" id="simple_product" value="0" />
+			<input type="radio" name="type_product" id="simple_product" value="{Product::PTYPE_SIMPLE}" />
 			{l s='Product'}
 		</label>
 		<label style="font-weight:normal;width:100px;text-align:center;">
-			<input type="radio" name="type_product" id="pack_product" value="1" />
+			<input type="radio" name="type_product" id="pack_product" value="{Product::PTYPE_PACK}" {if $is_pack}checked="checked"{/if} />
 			{l s='Pack'}
 		</label>
 		<label style="font-weight:normal;width:500px;text-align:center;">
-			<input type="radio" name="type_product" id="virtual_product" value="2" />
+			<input type="radio" name="type_product" id="virtual_product" value="{Product::PTYPE_VIRTUAL}" />
 			{l s='Virtual Product (services, booking and downloadable products)'}
 		</label>
 	</div>
diff --git a/classes/Product.php b/classes/Product.php
index 02c556d20..ced90e453 100644
--- a/classes/Product.php
+++ b/classes/Product.php
@@ -365,6 +365,12 @@ class ProductCore extends ObjectModel
 
 	const CUSTOMIZE_FILE = 0;
 	const CUSTOMIZE_TEXTFIELD = 1;
+	
+	
+	// Note:  prefix is "PTYPE" because TYPE_ is used in ObjectModel (definition)
+	const PTYPE_SIMPLE = 0;
+	const PTYPE_PACK = 1;
+	const PTYPE_VIRTUAL = 2;
 
 	public function __construct($id_product = null, $full = false, $id_lang = null, $id_shop = null, Context $context = null)
 	{
diff --git a/controllers/admin/AdminProductsController.php b/controllers/admin/AdminProductsController.php
index b046fe02e..840574899 100644
--- a/controllers/admin/AdminProductsController.php
+++ b/controllers/admin/AdminProductsController.php
@@ -1398,6 +1398,7 @@ class AdminProductsControllerCore extends AdminController
 		$object = new $this->className();
 		$this->_removeTaxFromEcotax();
 		$this->copyFromPost($object, $this->table);
+
 		if ($object->add())
 		{
 			$this->addCarriers();
@@ -1421,7 +1422,7 @@ class AdminProductsControllerCore extends AdminController
 				}
 
 				// If the product is virtual, set out_of_stock = 1 (allow sales when out of stock)
-				if (Tools::getValue('type_product') == 2)
+				if (Tools::getValue('type_product') == Product::PTYPE_VIRTUAL)
 					StockAvailable::setProductOutOfStock($object->id, 1);
 				else
 					StockAvailable::setProductOutOfStock($object->id, 2);
@@ -1546,6 +1547,7 @@ class AdminProductsControllerCore extends AdminController
 	public function checkProduct()
 	{
 		$className = 'Product';
+		// @todo : the call_user_func seems to contains only statics values (clasName = "Product")
 		$rules = call_user_func(array($this->className, 'getValidationRules'), $this->className);
 		$default_language = new Language((int)(Configuration::get('PS_LANG_DEFAULT')));
 		$languages = Language::getLanguages(false);
@@ -3843,12 +3845,19 @@ class AdminProductsControllerCore extends AdminController
 		$this->tpl_form_vars['input_namepack_items'] = $input_namepack_items;
 	}
 
+	/**
+	 * delete all items in pack, then check if type_product value is 2.
+	 * if yes, add the pack items from input "inputPackItems"
+	 * 
+	 * @param Product $product 
+	 * @return boolean
+	 */
 	public function updatePackItems($product)
 	{
 		Pack::deleteItems($product->id);
 
 		// lines format: QTY x ID-QTY x ID
-		if (Tools::getValue('type_product') == 1)
+		if (Tools::getValue('type_product') == Product::PTYPE_PACK)
 		{
 			$items = Tools::getValue('inputPackItems');
 			$lines = array_unique(explode('-', $items));