diff --git a/htdocs/categories/class/categorie.class.php b/htdocs/categories/class/categorie.class.php
index 99686eed40d..5485cb31db6 100644
--- a/htdocs/categories/class/categorie.class.php
+++ b/htdocs/categories/class/categorie.class.php
@@ -889,17 +889,14 @@ class Categorie
 		}
 		else 										// mother_id undefined (so it's root)
 		{
-			/* We have to select any rowid from llx_categorie which which category's type and label
-			 * are equals to those of the calling category, AND which doesn't exist in categorie association
-			 * as children (rowid != fk_categorie_fille)
-			 */
-			$sql = "SELECT c.rowid";
-			$sql.= " FROM ".MAIN_DB_PREFIX."categorie as c ";
-			$sql.= " JOIN ".MAIN_DB_PREFIX."categorie_association as ca";
-			$sql.= " ON c.rowid!=ca.fk_categorie_fille";
-			$sql.= " WHERE c.type=".$this->type;
-			$sql.= " AND c.label='".$this->db->escape($this->label)."'";
-			$sql.= " AND c.entity IN (".getEntity('category',1).")";
+			/* We have to select any rowid from llx_categorie that is not at root level
+			 */
+			$sql = "SELECT c.rowid";
+			$sql.= " FROM ".MAIN_DB_PREFIX."categorie as c ";
+			$sql.= " WHERE c.type=".$this->type;
+			$sql.= " AND c.label='".$this->db->escape($this->label)."'";
+			$sql.= " AND c.entity IN (".getEntity('category',1).")";
+			$sql.= " AND c.rowid NOT IN (SELECT ca.fk_categorie_fille FROM ".MAIN_DB_PREFIX."categorie_association as ca)";
 		}
 		dol_syslog(get_class($this)."::already_exists sql=".$sql, LOG_DEBUG);
 		$resql = $this->db->query($sql);
diff --git a/test/phpunit/CategorieTest.php b/test/phpunit/CategorieTest.php
index caa02a30538..5ceab0f40cd 100755
--- a/test/phpunit/CategorieTest.php
+++ b/test/phpunit/CategorieTest.php
@@ -131,7 +131,14 @@ class CategorieTest extends PHPUnit_Framework_TestCase
 		// We create a category
 		$localobject=new Categorie($this->savdb);
     	$localobject->initAsSpecimen();
-		$resultFirstCreate=$localobject->create($user);
+
+    	// Check it does not exist (return 0)
+    	$resultCheck=$localobject->already_exists();
+    	print __METHOD__." resultCheck=".$resultCheck."\n";
+    	$this->assertEquals(0, $resultCheck);
+
+    	// Create
+    	$resultFirstCreate=$localobject->create($user);
     	print __METHOD__." resultFirstCreate=".$resultFirstCreate."\n";
     	$this->assertGreaterThan(0, $resultFirstCreate);
 
@@ -139,8 +146,9 @@ class CategorieTest extends PHPUnit_Framework_TestCase
 		$localobject2=new Categorie($this->savdb);
     	$localobject2->initAsSpecimen();
 
+    	// Check it does exist (return 1)
     	$resultCheck=$localobject2->already_exists();
-    	print __METHOD__." resultCheck=".$resultCheck."\n";
+    	print __METHOD__." resultCheck=".$resultCheck."\n";
     	$this->assertGreaterThan(0, $resultCheck);
 
     	$resultSecondCreate=$localobject2->create($user);