diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/BaseCalendar.java b/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/BaseCalendar.java
index d3fd9fba0..dd7701426 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/BaseCalendar.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/BaseCalendar.java
@@ -836,23 +836,30 @@ public class BaseCalendar extends BaseEntity implements IWorkHours {
     @Override
     public boolean thereAreAvailableHoursFrom(LocalDate start,
             ResourcesPerDay resourcesPerDay, int hoursToAllocate) {
+        AvailabilityTimeLine availability = getAvailabilityFrom(start);
+        return thereAreHoursOn(availability, resourcesPerDay, hoursToAllocate);
+    }
+
+    @Override
+    public boolean thereAreHoursOn(AvailabilityTimeLine availability,
+            ResourcesPerDay resourcesPerDay, int hoursToAllocate) {
         if (hoursToAllocate == 0) {
             return true;
         }
         if (resourcesPerDay.isZero()) {
             return false;
         }
-        AvailabilityTimeLine availability = getAvailabilityFrom(start);
+        addInvaliditiesDerivedFromCalendar(availability);
         List<Interval> validPeriods = availability.getValidPeriods();
         if (validPeriods.isEmpty()) {
             return false;
         }
+
         Interval last = getLast(validPeriods);
         Interval first = validPeriods.get(0);
-        assert !first.getStart().equals(StartOfTime.create()) : "the start cannot be start of time,"
-                + " since a start is provided";
+        final boolean isOpenEnded = last.getEnd().equals(EndOfTime.create())
+                || first.getStart().equals(StartOfTime.create());
 
-        boolean isOpenEnded = last.getEnd().equals(EndOfTime.create());
         return isOpenEnded
                 || thereAreHoursOn(hoursToAllocate, resourcesPerDay,
                         validPeriods);
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/CombinedWorkHours.java b/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/CombinedWorkHours.java
index 7f46c8457..dd82f59ac 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/CombinedWorkHours.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/CombinedWorkHours.java
@@ -84,6 +84,18 @@ public abstract class CombinedWorkHours implements IWorkHours {
         }
         return true;
     }
+
+    @Override
+    public boolean thereAreHoursOn(AvailabilityTimeLine availability,
+            ResourcesPerDay resourcesPerDay, int hoursToAllocate) {
+        for (IWorkHours each : workHours) {
+            if (!each.thereAreHoursOn(availability, resourcesPerDay,
+                    hoursToAllocate)) {
+                return false;
+            }
+        }
+        return true;
+    }
 }
 
 class Min extends CombinedWorkHours {
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/IWorkHours.java b/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/IWorkHours.java
index 1f9ec2de9..197e7b4d3 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/IWorkHours.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/IWorkHours.java
@@ -43,6 +43,9 @@ public interface IWorkHours {
      */
     public Integer getCapacityAt(LocalDate date);
 
+    public boolean thereAreHoursOn(AvailabilityTimeLine availability,
+            ResourcesPerDay resourcesPerDay, int hoursToAllocate);
+
     public boolean thereAreAvailableHoursFrom(LocalDate date,
             ResourcesPerDay resourcesPerDay, int hours);
 
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/SameWorkHoursEveryDay.java b/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/SameWorkHoursEveryDay.java
index b8a3ec988..31786b727 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/SameWorkHoursEveryDay.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/SameWorkHoursEveryDay.java
@@ -56,4 +56,9 @@ public class SameWorkHoursEveryDay implements IWorkHours {
         return true;
     }
 
+    @Override
+    public boolean thereAreHoursOn(AvailabilityTimeLine availability,
+            ResourcesPerDay resourcesPerDay, int hoursToAllocate) {
+        return true;
+    }
 }
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 e20031936..de8350abb 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
@@ -35,6 +35,7 @@ import java.util.Map.Entry;
 import org.apache.commons.lang.Validate;
 import org.hibernate.validator.NotNull;
 import org.joda.time.LocalDate;
+import org.navalplanner.business.calendars.entities.AvailabilityTimeLine;
 import org.navalplanner.business.calendars.entities.BaseCalendar;
 import org.navalplanner.business.calendars.entities.IWorkHours;
 import org.navalplanner.business.calendars.entities.SameWorkHoursEveryDay;
@@ -560,6 +561,16 @@ public abstract class ResourceAllocation<T extends DayAssignment> extends
                 return getTaskCalendar().thereAreAvailableHoursFrom(date,
                         resourcesPerDay, hours);
             }
+
+            @Override
+            public boolean thereAreHoursOn(AvailabilityTimeLine availability,
+                    ResourcesPerDay resourcesPerDay, int hoursToAllocate) {
+                if (getTaskCalendar() == null) {
+                    return true;
+                }
+                return getTaskCalendar().thereAreHoursOn(availability,
+                        resourcesPerDay, hoursToAllocate);
+            }
         };
     }