diff --git a/navalplanner-webapp/src/main/java/org/navalplanner/web/planner/allocation/ResourceAllocationModel.java b/navalplanner-webapp/src/main/java/org/navalplanner/web/planner/allocation/ResourceAllocationModel.java
index e55163a12..e03d455c9 100644
--- a/navalplanner-webapp/src/main/java/org/navalplanner/web/planner/allocation/ResourceAllocationModel.java
+++ b/navalplanner-webapp/src/main/java/org/navalplanner/web/planner/allocation/ResourceAllocationModel.java
@@ -317,7 +317,9 @@ public class ResourceAllocationModel implements IResourceAllocationModel {
     private void reattachResource(Resource resource) {
         resourceDAO.reattach(resource);
         reattachCriterionSatisfactions(resource.getCriterionSatisfactions());
-        calendarDAO.reattachUnmodifiedEntity(resource.getCalendar());
+        if (resource.getCalendar() != null) {
+            calendarDAO.reattachUnmodifiedEntity(resource.getCalendar());
+        }
         for (DayAssignment dayAssignment : resource.getAssignments()) {
             Hibernate.initialize(dayAssignment);
         }