diff --git a/src/models/element/ElementLinkType.php b/src/models/element/ElementLinkType.php
index c15465e..7b8b3f6 100644
--- a/src/models/element/ElementLinkType.php
+++ b/src/models/element/ElementLinkType.php
@@ -152,7 +152,7 @@ public function toRecordAttributes(Link $model): array {
    * @return void
    * @noinspection PhpUnused (Validator)
    */
-  public function validateElementType() {
+  public function validateElementType(): void {
     if (!is_subclass_of($this->elementType, ElementInterface::class)) {
       $this->addError('elementType', 'Element type must be a class implementing ElementInterface');
     }