diff --git a/htdocs/main.inc.php b/htdocs/main.inc.php
index 3cbef0d799e..e00c1887fa7 100644
--- a/htdocs/main.inc.php
+++ b/htdocs/main.inc.php
@@ -1428,6 +1428,7 @@ function top_httphead($contenttype = 'text/html', $forcenocache = 0)
 		$contentsecuritypolicy = empty($conf->global->MAIN_HTTP_CONTENT_SECURITY_POLICY) ? '' : $conf->global->MAIN_HTTP_CONTENT_SECURITY_POLICY;
 
 		if (!is_object($hookmanager)) {
+			include_once DOL_DOCUMENT_ROOT.'/core/class/hookmanager.class.php';
 			$hookmanager = new HookManager($db);
 		}
 		$hookmanager->initHooks(array("main"));