diff --git a/Services/Tree/classes/class.ilMaterializedPathTree.php b/Services/Tree/classes/class.ilMaterializedPathTree.php
index a0ee268187f6..e3c00f63fe0f 100644
--- a/Services/Tree/classes/class.ilMaterializedPathTree.php
+++ b/Services/Tree/classes/class.ilMaterializedPathTree.php
@@ -583,7 +583,7 @@ public function getSubtreeInfo(int $a_endnode_id): array
      */
     public function validateParentRelations(): array
     {
-        $query = 'select child from ' . $this->getTree()->getTreeTable() . ' child where not exists ' .
+        $query = 'select ' . $this->getTree()->getTreePk() .', child from ' . $this->getTree()->getTreeTable() . ' child where not exists ' .
             '( ' .
             'select child from ' . $this->getTree()->getTreeTable() . ' parent where child.parent = parent.child and ' .
             '(child.path BETWEEN parent.path AND CONCAT(parent.path,' . $this->db->quote('Z', 'text') . ') )' . ')' .
diff --git a/Services/Tree/classes/class.ilNestedSetTree.php b/Services/Tree/classes/class.ilNestedSetTree.php
index 5d40b8f1c966..c9b42161834c 100644
--- a/Services/Tree/classes/class.ilNestedSetTree.php
+++ b/Services/Tree/classes/class.ilNestedSetTree.php
@@ -955,7 +955,7 @@ public function getSubtreeInfo(int $a_endnode_id): array
      */
     public function validateParentRelations(): array
     {
-        $query = 'select child from ' . $this->getTree()->getTreeTable() . ' child where not exists ' .
+        $query = 'select ' . $this->getTree()->getTreePk() .', child from ' . $this->getTree()->getTreeTable() . ' child where not exists ' .
             '( ' .
             'select child from ' . $this->getTree()->getTreeTable() . ' parent where child.parent = parent.child and (parent.lft < child.lft) and (parent.rgt > child.rgt) ' .
             ')' .