diff --git a/htdocs/compta/facture/class/facture.class.php b/htdocs/compta/facture/class/facture.class.php
index 02889c4c4ef..08ca9b6bb53 100644
--- a/htdocs/compta/facture/class/facture.class.php
+++ b/htdocs/compta/facture/class/facture.class.php
@@ -2267,7 +2267,6 @@ class Facture extends CommonInvoice
 				$sql .= ' SET fk_facture = NULL, fk_facture_line = NULL';
 				$sql .= ' WHERE fk_facture_line IN ('.$this->db->sanitize(join(',', $list_rowid_det)).')';
 
-				dol_syslog(get_class($this)."::delete", LOG_DEBUG);
 				if (!$this->db->query($sql)) {
 					$this->error = $this->db->error()." sql=".$sql;
 					$this->errors[] = $this->error;
@@ -2276,6 +2275,30 @@ class Facture extends CommonInvoice
 				}
 			}
 
+			// Remove other links to the deleted invoice
+
+			$sql = 'UPDATE '.MAIN_DB_PREFIX.'eventorganization_conferenceorboothattendee';
+			$sql .= ' SET fk_facture = NULL';
+			$sql .= ' WHERE fk_facture = '.((int) $rowid);
+
+			if (!$this->db->query($sql)) {
+				$this->error = $this->db->error()." sql=".$sql;
+				$this->errors[] = $this->error;
+				$this->db->rollback();
+				return -5;
+			}
+
+			$sql = 'UPDATE '.MAIN_DB_PREFIX.'projet_task_time';
+			$sql .= ' SET invoice_id = NULL, invoice_line_id = NULL';
+			$sql .= ' WHERE invoice_id = '.((int) $rowid);
+
+			if (!$this->db->query($sql)) {
+				$this->error = $this->db->error()." sql=".$sql;
+				$this->errors[] = $this->error;
+				$this->db->rollback();
+				return -5;
+			}
+
 			// If we decrease stock on invoice validation, we increase back if a warehouse id was provided
 			if ($this->type != self::TYPE_DEPOSIT && $result >= 0 && !empty($conf->stock->enabled) && !empty($conf->global->STOCK_CALCULATE_ON_BILL) && $idwarehouse != -1) {
 				require_once DOL_DOCUMENT_ROOT.'/product/stock/class/mouvementstock.class.php';
@@ -2299,17 +2322,13 @@ class Facture extends CommonInvoice
 			// Invoice line extrafileds
 			$main = MAIN_DB_PREFIX.'facturedet';
 			$ef = $main."_extrafields";
-			$sqlef = "DELETE FROM $ef WHERE fk_object IN (SELECT rowid FROM ".$main." WHERE fk_facture = ".((int) $rowid).")";
+			$sqlef = "DELETE FROM ".$ef." WHERE fk_object IN (SELECT rowid FROM ".$main." WHERE fk_facture = ".((int) $rowid).")";
 			// Delete invoice line
 			$sql = 'DELETE FROM '.MAIN_DB_PREFIX.'facturedet WHERE fk_facture = '.((int) $rowid);
 
-			dol_syslog(get_class($this)."::delete", LOG_DEBUG);
-
 			if ($this->db->query($sqlef) && $this->db->query($sql) && $this->delete_linked_contact()) {
 				$sql = 'DELETE FROM '.MAIN_DB_PREFIX.'facture WHERE rowid = '.((int) $rowid);
 
-				dol_syslog(get_class($this)."::delete", LOG_DEBUG);
-
 				$resql = $this->db->query($sql);
 				if ($resql) {
 					// Delete record into ECM index (Note that delete is also done when deleting files with the dol_delete_dir_recursive
diff --git a/htdocs/install/mysql/tables/llx_eventorganization_conferenceorboothattendee.sql b/htdocs/install/mysql/tables/llx_eventorganization_conferenceorboothattendee.sql
index 6d01cf4bba1..b505f8f6a31 100644
--- a/htdocs/install/mysql/tables/llx_eventorganization_conferenceorboothattendee.sql
+++ b/htdocs/install/mysql/tables/llx_eventorganization_conferenceorboothattendee.sql
@@ -21,6 +21,7 @@ CREATE TABLE llx_eventorganization_conferenceorboothattendee(
 	fk_soc integer,
 	fk_actioncomm integer,
 	fk_project integer NOT NULL,
+	fk_invoice integer NULL,
 	email varchar(100),
 	date_subscription datetime, 
 	amount double DEFAULT NULL,