diff --git a/htdocs/exports/class/export.class.php b/htdocs/exports/class/export.class.php
index f6ef6a27e2b..da184f27574 100644
--- a/htdocs/exports/class/export.class.php
+++ b/htdocs/exports/class/export.class.php
@@ -637,6 +637,7 @@ class Export
 							// Operation GETNUMOPENDAYS (for Holiday module)
 							elseif ($this->array_export_special[$indice][$key]=='getNumOpenDays')
 							{
+								include_once DOL_DOCUMENT_ROOT.'/core/lib/date.lib.php';
 								//$alias=$this->array_export_alias[$indice][$key];
 								$alias=str_replace(array('.', '-','(',')'), '_', $key);
 								$obj->$alias=num_open_day(dol_stringtotime($obj->d_date_debut, 1), dol_stringtotime($obj->d_date_fin, 1), 0, 1, $obj->d_halfday, $mysoc->country_code);