diff --git a/op/op.UpdateDocument.php b/op/op.UpdateDocument.php
index dd4e05cd2..e633f44ff 100644
--- a/op/op.UpdateDocument.php
+++ b/op/op.UpdateDocument.php
@@ -283,10 +283,38 @@ default:
 		$attributes = $_POST["attributes_version"];
 		foreach($attributes as $attrdefid=>$attribute) {
 			$attrdef = $dms->getAttributeDefinition($attrdefid);
+			if(null === ($ret = $controller->callHook('validateAttribute', $attrdef, $attribute))) {
 			if($attribute) {
 				switch($attrdef->getType()) {
 				case SeedDMS_Core_AttributeDefinition::type_date:
-					$attribute = date('Y-m-d', makeTsFromDate($attribute));
+					if(is_array($attribute))
+						$attribute = array_map(fn($value): string => date('Y-m-d', makeTsFromDate($value)), $attribute);
+					else
+						$attribute = date('Y-m-d', makeTsFromDate($attribute));
+					break;
+				case SeedDMS_Core_AttributeDefinition::type_folder:
+					if(is_array($attribute))
+						$attribute = array_map(fn($value): object => $dms->getFolder((int) $value), $attribute);
+					else
+						$attribute = $dms->getFolder((int) $attribute);
+					break;
+				case SeedDMS_Core_AttributeDefinition::type_document:
+					if(is_array($attribute))
+						$attribute = array_map(fn($value): object => $dms->getDocument((int) $value), $attribute);
+					else
+						$attribute = $dms->getDocument((int) $attribute);
+					break;
+				case SeedDMS_Core_AttributeDefinition::type_user:
+					if(is_array($attribute))
+						$attribute = array_map(fn($value): object => $dms->getUser((int) $value), $attribute);
+					else
+						$attribute = $dms->getUser((int) $attribute);
+					break;
+				case SeedDMS_Core_AttributeDefinition::type_group:
+					if(is_array($attribute))
+						$attribute = array_map(fn($value): object => $dms->getGroup((int) $value), $attribute);
+					else
+						$attribute = $dms->getGroup((int) $attribute);
 					break;
 				}
 				if(!$attrdef->validate($attribute, null, true)) {
@@ -296,6 +324,10 @@ default:
 			} elseif($attrdef->getMinValues() > 0) {
 				UI::exitError(getMLText("document_title", array("documentname" => $document->getName())),getMLText("attr_min_values", array("attrname"=>$attrdef->getName())));
 			}
+			} else {
+				if($ret === false)
+					return false;
+			}
 		}
 	} else {
 		$attributes = array();