diff --git a/forms/CheckboxSetField.php b/forms/CheckboxSetField.php
index 07e6d100d..84f976408 100644
--- a/forms/CheckboxSetField.php
+++ b/forms/CheckboxSetField.php
@@ -181,15 +181,16 @@ class CheckboxSetField extends OptionsetField {
 	 * @param DataObject $record The record to save into
 	 */
 	function saveInto(DataObject $record) {
-		$fieldname = $this->name ;
-		if($fieldname && $record && ($record->has_many($fieldname) || $record->many_many($fieldname))) {
+		$fieldname = $this->name;
+		$relation = ($fieldname && $record && $record->hasMethod($fieldname)) ? $record->$fieldname() : null;
+		if($fieldname && $record && $relation && $relation instanceof RelationList) {
 			$idList = array();
 			if($this->value) foreach($this->value as $id => $bool) {
 			   if($bool) {
 					$idList[] = $id;
 				}
 			}
-			$record->$fieldname()->setByIDList($idList);
+			$relation->setByIDList($idList);
 		} elseif($fieldname && $record) {
 			if($this->value) {
 				$this->value = str_replace(',', '{comma}', $this->value);
diff --git a/forms/ListboxField.php b/forms/ListboxField.php
index 42aeb3291..c52df9f8b 100644
--- a/forms/ListboxField.php
+++ b/forms/ListboxField.php
@@ -172,10 +172,11 @@ class ListboxField extends DropdownField {
 	function saveInto(DataObject $record) {
 		if($this->multiple) {
 			$fieldname = $this->name;
-			if($fieldname && $record && ($record->has_many($fieldname) || $record->many_many($fieldname))) {
+			$relation = ($fieldname && $record && $record->hasMethod($fieldname)) ? $record->$fieldname() : null;
+			if($fieldname && $record && $relation && $relation instanceof RelationList) {
 				$idList = (is_array($this->value)) ? array_values($this->value) : array();
 				if(!$record->ID) $record->write(); // record needs to have an ID in order to set relationships
-				$record->$fieldname()->setByIDList($idList);
+				$relation->setByIDList($idList);
 			} elseif($fieldname && $record) {
 				if($this->value) {
 					$this->value = str_replace(',', '{comma}', $this->value);