diff --git a/navalplanner-webapp/src/main/java/org/navalplanner/web/calendars/BaseCalendarEditionController.java b/navalplanner-webapp/src/main/java/org/navalplanner/web/calendars/BaseCalendarEditionController.java
index d956bcbfb..6357bd976 100644
--- a/navalplanner-webapp/src/main/java/org/navalplanner/web/calendars/BaseCalendarEditionController.java
+++ b/navalplanner-webapp/src/main/java/org/navalplanner/web/calendars/BaseCalendarEditionController.java
@@ -949,6 +949,9 @@ public abstract class BaseCalendarEditionController extends
         if (isDerived()) {
             Combobox parentCalendars = (Combobox) createNewVersionWindow
                     .getFellow("parentCalendars");
+            if (parentCalendars.getSelectedItem() == null) {
+                return;
+            }
             selected = (BaseCalendar) parentCalendars.getSelectedItem()
                     .getValue();
         }
diff --git a/navalplanner-webapp/src/main/webapp/calendars/_createNewVersion.zul b/navalplanner-webapp/src/main/webapp/calendars/_createNewVersion.zul
index 31217254f..4c55a1d05 100644
--- a/navalplanner-webapp/src/main/webapp/calendars/_createNewVersion.zul
+++ b/navalplanner-webapp/src/main/webapp/calendars/_createNewVersion.zul
@@ -28,6 +28,7 @@
                       <label value="${i18n:_('Type')}:"/>
                       <label value="@{calendarController.editionController.calendarType}"/>
                       <combobox id="parentCalendars"
+                        constraint="no empty:${i18n:_('cannot be null or empty')}"
                         model="@{calendarController.editionController.parentCalendars}">
                         <comboitem self="@{each='baseCalnedar'}"
                           value="@{baseCalnedar}" label="@{baseCalnedar.name}" />