diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/ResourceAllocation.java b/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/ResourceAllocation.java
index 1955a8241..b0c492de4 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/ResourceAllocation.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/ResourceAllocation.java
@@ -1,5 +1,6 @@
 package org.navalplanner.business.planner.entities;
 
+import java.math.BigDecimal;
 import java.util.ArrayList;
 import java.util.List;
 
@@ -41,11 +42,26 @@ public abstract class ResourceAllocation<T extends DayAssignment> extends
             Validate.noNullElements(resourceAllocations);
             checkNoOneHasNullTask(resourceAllocations);
             checkAllHaveSameTask(resourceAllocations);
+            checkNoAllocationWithZeroResourcesPerDay(resourceAllocations);
             this.resourceAllocations = resourceAllocations;
             this.task = resourceAllocations.get(0).getResourceAllocation()
                     .getTask();
         }
 
+        private static void checkNoAllocationWithZeroResourcesPerDay(
+                List<ResourceAllocationWithDesiredResourcesPerDay> allocations) {
+            for (ResourceAllocationWithDesiredResourcesPerDay r : allocations) {
+                if (isZero(r.getResourcesPerDay().getAmount())) {
+                    throw new IllegalArgumentException(
+                            "all resources per day must be no zero");
+                }
+            }
+        }
+
+        private static boolean isZero(BigDecimal amount) {
+            return amount.movePointRight(amount.scale()).intValue() == 0;
+        }
+
         private static void checkNoOneHasNullTask(
                 List<ResourceAllocationWithDesiredResourcesPerDay> allocations) {
             for (ResourceAllocationWithDesiredResourcesPerDay resourceAllocationWithDesiredResourcesPerDay : allocations) {
@@ -72,6 +88,7 @@ public abstract class ResourceAllocation<T extends DayAssignment> extends
 
         public AllocationsAndResourcesCurried withResources(
                 List<Resource> resources) {
+            Validate.noNullElements(resources);
             return new AllocationsAndResourcesCurried(task, resources,
                     resourceAllocations);
         }
@@ -93,6 +110,9 @@ public abstract class ResourceAllocation<T extends DayAssignment> extends
         }
 
         public LocalDate untilAllocating(int hoursToAllocate) {
+            if (thereIsGenericAllocation()) {
+                Validate.notEmpty(resources, "there must exist workers");
+            }
             AllocatorForSpecifiedResourcesPerDayAndHours allocator = new AllocatorForSpecifiedResourcesPerDayAndHours(
                     task, resources, allocations) {
 
@@ -117,6 +137,15 @@ public abstract class ResourceAllocation<T extends DayAssignment> extends
             return allocator.untilAllocating(hoursToAllocate);
         }
 
+        private boolean thereIsGenericAllocation() {
+            for (ResourceAllocationWithDesiredResourcesPerDay r : allocations) {
+                if (r.getResourceAllocation() instanceof GenericResourceAllocation) {
+                    return true;
+                }
+            }
+            return false;
+        }
+
         public void allocateOnTaskLength() {
             AllocatorForTaskDurationAndSpecifiedResourcesPerDay allocator = new AllocatorForTaskDurationAndSpecifiedResourcesPerDay(
                     allocations, resources);
diff --git a/navalplanner-business/src/test/java/org/navalplanner/business/test/planner/entities/AllocationUntilFillingHoursTest.java b/navalplanner-business/src/test/java/org/navalplanner/business/test/planner/entities/AllocationUntilFillingHoursTest.java
index 08c8cbc3e..3415bec57 100644
--- a/navalplanner-business/src/test/java/org/navalplanner/business/test/planner/entities/AllocationUntilFillingHoursTest.java
+++ b/navalplanner-business/src/test/java/org/navalplanner/business/test/planner/entities/AllocationUntilFillingHoursTest.java
@@ -129,6 +129,32 @@ public class AllocationUntilFillingHoursTest {
         assertThat(secondSpecific.getAssignments(), haveHours(8, 8));
     }
 
+    @Test(expected = IllegalArgumentException.class)
+    public void withGenericAllocationWithNoResourcesPerDay() {
+        givenWorkers(1);
+        givenGenericAllocation(ResourcesPerDay.amount(0));
+        ResourceAllocation.allocating(allocations).withResources(resources)
+                .untilAllocating(100);
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void cannotDoAGenericAllocationWithoutWorkers() {
+        givenWorkers(0);
+        givenGenericAllocation(ResourcesPerDay.amount(2));
+        ResourceAllocation.allocating(allocations)
+                .withResources(resources)
+                .untilAllocating(100);
+
+    }
+
+    @Test
+    public void withoutWorkersYouCanDoSpecificAllocation() {
+        givenWorkers(0);
+        givenSpecificAllocations(ResourcesPerDay.amount(2));
+        ResourceAllocation.allocating(allocations).withResources(resources)
+                .untilAllocating(100);
+    }
+
     private void givenGenericAllocation(ResourcesPerDay resourcesPerDay) {
         createTaskIfNotCreatedYet();
         allocations.add(new ResourceAllocationWithDesiredResourcesPerDay(