diff --git a/htdocs/categories/class/categorie.class.php b/htdocs/categories/class/categorie.class.php
index 7a7cc186a6d..fe00cf3a4cf 100644
--- a/htdocs/categories/class/categorie.class.php
+++ b/htdocs/categories/class/categorie.class.php
@@ -125,6 +125,7 @@ class Categorie
 	 * 	@return	int 				-1 : erreur SQL
 	 *          					-2 : nouvel ID inconnu
 	 *          					-3 : categorie invalide
+	 * 								-4 : category already exists
 	 */
 	function create($user='')
 	{
@@ -141,7 +142,7 @@ class Categorie
 		{
 			$this->error=$langs->trans("ImpossibleAddCat");
 			$this->error.=" : ".$langs->trans("CategoryExistsAtSameLevel");
-			return -1;
+			return -4;
 		}
 
 		$sql = "INSERT INTO ".MAIN_DB_PREFIX."categorie (label, description,";
@@ -176,7 +177,7 @@ class Categorie
 					if($this->add_fille() < 0)
 					{
 						$this->error=$langs->trans("ImpossibleAssociateCategory");
-						return -1;
+						return -3;
 					}
 				}
 
diff --git a/test/phpunit/CategorieTest.php b/test/phpunit/CategorieTest.php
index 24693fdac20..f87a2c29d44 100755
--- a/test/phpunit/CategorieTest.php
+++ b/test/phpunit/CategorieTest.php
@@ -129,12 +129,16 @@ class CategorieTest extends PHPUnit_Framework_TestCase
 
 		$localobject=new Categorie($this->savdb);
     	$localobject->initAsSpecimen();
-    	$result=$localobject->create($user);
 
+		// We create category
+    	$result=$localobject->create($user);
     	$this->assertLessThan($result, 0);
     	print __METHOD__." result=".$result."\n";
 
-    	// TODO Add test on error when creating duplicate
+		// We try to create same category again
+    	$result=$localobject->create($user);
+    	$this->assertLessThan($result, -4);
+    	print __METHOD__." result=".$result."\n";
 
 
     	return $result;