diff --git a/core/oqlclasstreebuilder.class.inc.php b/core/oqlclasstreebuilder.class.inc.php
index 236f9d684..2e25fb1dd 100644
--- a/core/oqlclasstreebuilder.class.inc.php
+++ b/core/oqlclasstreebuilder.class.inc.php
@@ -296,13 +296,11 @@ class OQLClassTreeBuilder
 								$oQBContextExpressions->AddCondition($oClassRestriction);
 							} elseif (($oKeyAttDef instanceof AttributeExternalKey) && $sKeyClass != $oKeyAttDef->GetTargetClass()) {
 								$sClassAttCode = 'finalclass';
-								if (MetaModel::IsValidAttCode($sKeyClass, $sClassAttCode)) {
-									$oClassListExpr = ListExpression::FromScalars(MetaModel::EnumChildClasses($sKeyClass,
-										ENUM_CHILD_CLASSES_ALL));
-									$oClassExpr = new FieldExpression($sClassAttCode, $sKeyClassAlias);
-									$oClassRestriction = new BinaryExpression($oClassExpr, 'IN', $oClassListExpr);
-									$oQBContextExpressions->AddCondition($oClassRestriction);
-								}
+								$oClassListExpr = ListExpression::FromScalars(MetaModel::EnumChildClasses($sKeyClass,
+									ENUM_CHILD_CLASSES_ALL));
+								$oClassExpr = new FieldExpression($sClassAttCode, $sKeyClassAlias);
+								$oClassRestriction = new BinaryExpression($oClassExpr, 'IN', $oClassListExpr);
+								$oQBContextExpressions->AddCondition($oClassRestriction);
 							}
 
 							// Translate prior to recursing