diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/common/Registry.java b/navalplanner-business/src/main/java/org/navalplanner/business/common/Registry.java
index f4f1ef81e..6c037228b 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/common/Registry.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/common/Registry.java
@@ -21,6 +21,7 @@
 package org.navalplanner.business.common;
 
 import org.navalplanner.business.advance.daos.IAdvanceTypeDAO;
+import org.navalplanner.business.costcategories.daos.ITypeOfWorkHoursDAO;
 import org.navalplanner.business.resources.daos.ICriterionTypeDAO;
 import org.navalplanner.business.resources.daos.IMachineDAO;
 import org.navalplanner.business.users.daos.IUserDAO;
@@ -57,6 +58,9 @@ public class Registry {
     @Autowired
     private IWorkReportTypeDAO workReportTypeDAO;
 
+    @Autowired
+    private ITypeOfWorkHoursDAO typeOfWorkHoursDAO;
+
     private Registry() {
     }
 
@@ -83,4 +87,9 @@ public class Registry {
     public static IWorkReportTypeDAO getWorkReportTypeDAO() {
         return getInstance().workReportTypeDAO;
     }
+
+    public static ITypeOfWorkHoursDAO getTypeOfWorkHoursDAO() {
+        return getInstance().typeOfWorkHoursDAO;
+    }
+
 }
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/daos/ITypeOfWorkHoursDAO.java b/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/daos/ITypeOfWorkHoursDAO.java
index 78d4b55d8..5e1c852fb 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/daos/ITypeOfWorkHoursDAO.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/daos/ITypeOfWorkHoursDAO.java
@@ -21,6 +21,7 @@
 package org.navalplanner.business.costcategories.daos;
 
 import org.navalplanner.business.common.daos.IGenericDAO;
+import org.navalplanner.business.common.exceptions.InstanceNotFoundException;
 import org.navalplanner.business.costcategories.entities.TypeOfWorkHours;
 
 /**
@@ -28,4 +29,11 @@ import org.navalplanner.business.costcategories.entities.TypeOfWorkHours;
  */
 public interface ITypeOfWorkHoursDAO extends IGenericDAO<TypeOfWorkHours, Long> {
 
+    TypeOfWorkHours findUniqueByCode(TypeOfWorkHours typeOfWorkHours)
+        throws InstanceNotFoundException;
+
+    TypeOfWorkHours findUniqueByCode(String code)
+        throws InstanceNotFoundException;
+
+    boolean existsByCode(TypeOfWorkHours typeOfWorkHours);
 }
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/daos/TypeOfWorkHoursDAO.java b/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/daos/TypeOfWorkHoursDAO.java
index 210188992..5cddb80ea 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/daos/TypeOfWorkHoursDAO.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/daos/TypeOfWorkHoursDAO.java
@@ -20,7 +20,13 @@
 
 package org.navalplanner.business.costcategories.daos;
 
+import static org.navalplanner.business.i18n.I18nHelper._;
+
+import org.apache.commons.lang.Validate;
+import org.hibernate.Criteria;
+import org.hibernate.criterion.Restrictions;
 import org.navalplanner.business.common.daos.GenericDAOHibernate;
+import org.navalplanner.business.common.exceptions.InstanceNotFoundException;
 import org.navalplanner.business.costcategories.entities.TypeOfWorkHours;
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.context.annotation.Scope;
@@ -32,6 +38,36 @@ import org.springframework.stereotype.Repository;
 @Repository
 @Scope(BeanDefinition.SCOPE_SINGLETON)
 public class TypeOfWorkHoursDAO extends GenericDAOHibernate<TypeOfWorkHours, Long> implements
-		ITypeOfWorkHoursDAO {
+        ITypeOfWorkHoursDAO {
 
+    @Override
+    public TypeOfWorkHours findUniqueByCode(TypeOfWorkHours typeOfWorkHours)
+                throws InstanceNotFoundException {
+
+        Validate.notNull(typeOfWorkHours);
+        return findUniqueByCode(typeOfWorkHours.getCode());
+    }
+
+    @Override
+    public TypeOfWorkHours findUniqueByCode(String code)
+            throws InstanceNotFoundException {
+
+        Criteria c = getSession().createCriteria(TypeOfWorkHours.class);
+        c.add(Restrictions.eq("code", code));
+
+        TypeOfWorkHours found = (TypeOfWorkHours) c.uniqueResult();
+        if (found==null)
+            throw new InstanceNotFoundException(found,
+                    _("Can't find a TypeOfWorkHours with code {0}", code));
+        return found;
+    }
+
+    @Override
+    public boolean existsByCode(TypeOfWorkHours typeOfWorkHours) {
+        try {
+            return findUniqueByCode(typeOfWorkHours) != null;
+        } catch (InstanceNotFoundException e) {
+            return false;
+        }
+    }
 }
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/entities/TypeOfWorkHours.java b/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/entities/TypeOfWorkHours.java
index b54578242..69dbe6a9d 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/entities/TypeOfWorkHours.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/entities/TypeOfWorkHours.java
@@ -22,8 +22,12 @@ package org.navalplanner.business.costcategories.entities;
 
 import java.math.BigDecimal;
 
+import org.hibernate.validator.AssertTrue;
 import org.hibernate.validator.NotEmpty;
 import org.navalplanner.business.common.BaseEntity;
+import org.navalplanner.business.common.Registry;
+import org.navalplanner.business.common.exceptions.InstanceNotFoundException;
+import org.navalplanner.business.costcategories.daos.ITypeOfWorkHoursDAO;
 
 /**
  * @author Jacobo Aragunde Perez <jaragunde@igalia.com>
@@ -89,4 +93,21 @@ public class TypeOfWorkHours extends BaseEntity {
     public void setEnabled(boolean enabled) {
         this.enabled = enabled;
     }
+
+    @AssertTrue(message="this code is already being used")
+    public boolean checkConstraintUniqueTypeOfWorkHoursCode() {
+
+        ITypeOfWorkHoursDAO dao = Registry.getTypeOfWorkHoursDAO();
+
+        if (isNewObject()) {
+            return !dao.existsByCode(this);
+        } else {
+            try {
+                TypeOfWorkHours type = dao.findUniqueByCode(code);
+                return type.getId().equals(getId());
+            } catch (InstanceNotFoundException e) {
+                return true;
+            }
+        }
+    }
 }
diff --git a/navalplanner-business/src/test/java/org/navalplanner/business/test/costcategories/daos/TypeOfWorkHoursDAOTest.java b/navalplanner-business/src/test/java/org/navalplanner/business/test/costcategories/daos/TypeOfWorkHoursDAOTest.java
index fbdd1ac5e..842da6ed8 100644
--- a/navalplanner-business/src/test/java/org/navalplanner/business/test/costcategories/daos/TypeOfWorkHoursDAOTest.java
+++ b/navalplanner-business/src/test/java/org/navalplanner/business/test/costcategories/daos/TypeOfWorkHoursDAOTest.java
@@ -89,4 +89,29 @@ public class TypeOfWorkHoursDAOTest {
         List<TypeOfWorkHours> list = typeOfWorkHoursDAO.list(TypeOfWorkHours.class);
         assertEquals(previous + 1, list.size());
     }
+
+    @Test
+    public void testFindTypesOfWorkHoursByCode() {
+        TypeOfWorkHours typeOfWorkHours = createValidTypeOfWorkHours();
+        typeOfWorkHoursDAO.save(typeOfWorkHours);
+        try {
+            TypeOfWorkHours found = typeOfWorkHoursDAO.findUniqueByCode(typeOfWorkHours.getCode());
+            assertNotNull(found);
+            assertTrue(found.equals(typeOfWorkHours));
+        }
+        catch (InstanceNotFoundException e) {
+
+        }
+    }
+
+    @Test(expected=InstanceNotFoundException.class)
+    public void testFindTypesOfWorkHoursByCodeException() throws InstanceNotFoundException{
+        TypeOfWorkHours typeOfWorkHours = createValidTypeOfWorkHours();
+        typeOfWorkHoursDAO.save(typeOfWorkHours);
+
+        typeOfWorkHoursDAO.remove(typeOfWorkHours.getId());
+
+        //this call should throw the exception
+        typeOfWorkHoursDAO.findUniqueByCode(typeOfWorkHours.getCode());
+    }
 }