diff --git a/public/tier1/utlrbtree.h b/public/tier1/utlrbtree.h
index ba287375..0b1c7324 100644
--- a/public/tier1/utlrbtree.h
+++ b/public/tier1/utlrbtree.h
@@ -587,7 +587,7 @@ inline	bool CUtlRBTree<T, I, L, M>::IsValidIndex( I i ) const
 	if ( !m_Elements.IsIdxValid( i ) )
 		return false;
 
-	if ( m_Elements.IsIdxAfter( i, m_LastAlloc ) )
+	if ( m_Elements.IsIdxAfter( i, m_Elements.Count() - 1 ) )
 		return false; // don't read values that have been allocated, but not constructed
 
 	return LeftChild(i) != i;