diff --git a/htdocs/categories/categorie.class.php b/htdocs/categories/categorie.class.php
index 13247d3f659..766c7ae06b8 100644
--- a/htdocs/categories/categorie.class.php
+++ b/htdocs/categories/categorie.class.php
@@ -566,11 +566,12 @@ class Categorie
 			return -1;
 		}
 
-		// On ajoute la propriete fullpath a tous les éléments
+		// We add the fulpath property to each elements of first level (no parent exists)
+		dolibarr_syslog("Categorie::get_full_arbo call to build_path_from_id_categ", LOG_DEBUG);
 		foreach($this->cats as $key => $val)
 		{
 			if (isset($motherof[$key])) continue;
-			$this->build_path_from_id_categ($key,0);	// Process a path of a root category (no mother exists)
+			$this->build_path_from_id_categ($key,0);	// Process a path of a root category (no parent exists)
 		}
 
 		dolibarr_syslog("Categorie::get_full_arbo dol_sort_array", LOG_DEBUG);
@@ -588,6 +589,8 @@ class Categorie
 	*/
 	function build_path_from_id_categ($id_categ,$protection=0)
 	{
+		dolibarr_syslog("Categorie::build_path_from_id_categ id_categ=".$id_categ." protection=".$protection, LOG_DEBUG);
+
 		// Defini fullpath
 		if (isset($this->cats[$id_categ]['id_mere']))
 		{
@@ -610,6 +613,13 @@ class Categorie
 		if (! is_array($this->cats[$id_categ]['id_children'])) return;
 		foreach($this->cats[$id_categ]['id_children'] as $key => $idchild)
 		{
+			// Protection when a category has itself as a child (should not happen)
+			if ($idchild == $id_categ)
+			{
+				dolibarr_syslog("Categorie::build_path_from_id_categ bad couple (".$idchild.",".$id_categ.") in association table: An entry should not have itself has child", LOG_WARNING);
+				continue;
+			}
+
 			$this->build_path_from_id_categ($idchild,$protection);
 		}
 		return;
diff --git a/mysql/migration/2.5.0-2.6.0.sql b/mysql/migration/2.5.0-2.6.0.sql
index 4a65edf5a4c..2864bf41313 100644
--- a/mysql/migration/2.5.0-2.6.0.sql
+++ b/mysql/migration/2.5.0-2.6.0.sql
@@ -59,3 +59,8 @@ alter table llx_user_param drop column page;
 
 alter table llx_commande_fournisseur_log add column comment varchar(255) NULL;
 
+delete from llx_categorie_association where fk_categorie_mere = fk_categorie_fille;
+
+
+-- Put at the end. Cas have duplicate values
+ALTER TABLE llx_categorie_association ADD UNIQUE INDEX uk_categorie_association (fk_categorie_mere, fk_categorie_fille);
diff --git a/mysql/tables/llx_categorie_association.key.sql b/mysql/tables/llx_categorie_association.key.sql
index 383899dea34..0a4d78a440c 100644
--- a/mysql/tables/llx_categorie_association.key.sql
+++ b/mysql/tables/llx_categorie_association.key.sql
@@ -24,5 +24,7 @@
 ALTER TABLE llx_categorie_association ADD INDEX idx_categorie_association_fk_categorie_mere (fk_categorie_mere);
 ALTER TABLE llx_categorie_association ADD INDEX idx_categorie_association_fk_categorie_fille (fk_categorie_fille);
 
+ALTER TABLE llx_categorie_association ADD UNIQUE INDEX uk_categorie_association (fk_categorie_mere, fk_categorie_fille);
+
 ALTER TABLE llx_categorie_association ADD CONSTRAINT fk_categorie_asso_fk_categorie_mere  FOREIGN KEY (fk_categorie_mere) REFERENCES llx_categorie (rowid);
 ALTER TABLE llx_categorie_association ADD CONSTRAINT fk_categorie_asso_fk_categorie_fille FOREIGN KEY (fk_categorie_fille) REFERENCES llx_categorie (rowid);