diff --git a/ganttzk/src/main/java/org/zkoss/ganttz/data/GanttDiagramGraph.java b/ganttzk/src/main/java/org/zkoss/ganttz/data/GanttDiagramGraph.java
index 0741febe9..e43361800 100644
--- a/ganttzk/src/main/java/org/zkoss/ganttz/data/GanttDiagramGraph.java
+++ b/ganttzk/src/main/java/org/zkoss/ganttz/data/GanttDiagramGraph.java
@@ -1135,7 +1135,7 @@ public class GanttDiagramGraph implements ICriticalPathCalculable<Task> {
     private Task getTopmostFor(Task task) {
         Task result = task;
         while (fromChildToParent.containsKey(result)) {
-            result = fromChildToParent.get(task);
+            result = fromChildToParent.get(result);
         }
         return result;
     }