diff --git a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/TaskDetail.java b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/TaskDetail.java
index 8d6701760..baa6c49fb 100644
--- a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/TaskDetail.java
+++ b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/TaskDetail.java
@@ -318,13 +318,14 @@ public class TaskDetail extends GenericForwardComposer {
     }
 
     public void updateBean() {
-        if (getEndDateBox().getValue().before(getStartDateBox().getValue())) {
-            updateComponents();
-            return;
+        Date begin = getStartDateBox().getValue();
+        Date end = getEndDateBox().getValue();
+        if (end.before(begin)) {
+            end = new Date(begin.getTime() + taskBean.getLengthMilliseconds());
         }
         taskBean.setName(getNameBox().getValue());
-        taskBean.setBeginDate(getStartDateBox().getValue());
-        taskBean.setEndDate(getEndDateBox().getValue());
+        taskBean.setBeginDate(begin);
+        taskBean.setEndDate(end);
     }
 
     private void updateComponents() {
diff --git a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/TaskBean.java b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/TaskBean.java
index cf4e7f081..b6715f3d1 100644
--- a/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/TaskBean.java
+++ b/navalplanner-gantt-zk/src/main/java/org/zkoss/ganttz/util/TaskBean.java
@@ -8,9 +8,7 @@ import java.util.Date;
  * This class contains the information of a task. It can be modified and
  * notifies of the changes to the interested parties. <br/>
  * Created at Apr 24, 2009
- *
  * @author Óscar González Fernández <ogonzalez@igalia.com>
- *
  */
 public class TaskBean {
 
@@ -81,6 +79,10 @@ public class TaskBean {
     }
 
     public void setLengthMilliseconds(long lengthMilliseconds) {
+        if (lengthMilliseconds < 0)
+            throw new IllegalArgumentException(
+                    "a task must not have a negative length. Received value: "
+                            + lengthMilliseconds);
         long previousValue = this.lengthMilliseconds;
         this.lengthMilliseconds = lengthMilliseconds;
         fundamentalProperties.firePropertyChange("lengthMilliseconds",
@@ -96,7 +98,8 @@ public class TaskBean {
         this.visibilityProperties.addPropertyChangeListener(listener);
     }
 
-    public void addFundamentalPropertiesChangeListener(PropertyChangeListener listener) {
+    public void addFundamentalPropertiesChangeListener(
+            PropertyChangeListener listener) {
         this.fundamentalProperties.addPropertyChangeListener(listener);
     }