diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/GenericResourceAllocation.java b/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/GenericResourceAllocation.java
index e0cfa8c33..b1c381df0 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/GenericResourceAllocation.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/GenericResourceAllocation.java
@@ -226,6 +226,9 @@ public class GenericResourceAllocation extends
 
     @Override
     public void mergeAssignmentsAndResourcesPerDay(ResourceAllocation<?> modifications) {
+        if (modifications == this) {
+            return;
+        }
         Validate.isTrue(modifications instanceof GenericResourceAllocation);
         mergeAssignments((GenericResourceAllocation) modifications);
         setResourcesPerDay(modifications.getResourcesPerDay());
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/SpecificResourceAllocation.java b/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/SpecificResourceAllocation.java
index 87f1ced97..de03b3dae 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/SpecificResourceAllocation.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/SpecificResourceAllocation.java
@@ -163,6 +163,9 @@ public class SpecificResourceAllocation extends
 
     @Override
     public void mergeAssignmentsAndResourcesPerDay(ResourceAllocation<?> modifications) {
+        if (modifications == this) {
+            return;
+        }
         Validate.isTrue(modifications instanceof SpecificResourceAllocation);
         mergeAssignments((SpecificResourceAllocation) modifications);
         setResourcesPerDay(modifications.getResourcesPerDay());