diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/materials/daos/MaterialCategoryDAO.java b/navalplanner-business/src/main/java/org/navalplanner/business/materials/daos/MaterialCategoryDAO.java
index 6a46a72cd..556f4c3c5 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/materials/daos/MaterialCategoryDAO.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/materials/daos/MaterialCategoryDAO.java
@@ -22,7 +22,7 @@ package org.navalplanner.business.materials.daos;
 
 import java.util.List;
 
-import org.hibernate.Criteria;
+import org.apache.commons.lang.StringUtils;
 import org.hibernate.criterion.Order;
 import org.hibernate.criterion.Restrictions;
 import org.navalplanner.business.common.daos.IntegrationEntityDAO;
@@ -72,14 +72,22 @@ public class MaterialCategoryDAO extends IntegrationEntityDAO<MaterialCategory>
     @Transactional(readOnly = true)
     public MaterialCategory findUniqueByName(String name)
             throws InstanceNotFoundException {
-        Criteria criteria = getSession().createCriteria(MaterialCategory.class);
-        criteria.add(Restrictions.eq("name", name).ignoreCase());
 
-        List<MaterialCategory> list = criteria.list();
-        if (list.size() != 1) {
-            throw new InstanceNotFoundException(name, MaterialCategory.class.getName());
+        if (StringUtils.isBlank(name)) {
+            throw new InstanceNotFoundException(null, getEntityClass()
+                    .getName());
+        }
+
+        MaterialCategory materialCategory = (MaterialCategory) getSession()
+                .createCriteria(MaterialCategory.class).add(
+                        Restrictions.eq("name", name.trim()).ignoreCase())
+                .uniqueResult();
+
+        if (materialCategory == null) {
+            throw new InstanceNotFoundException(name, getEntityClass().getName());
+        } else {
+            return materialCategory;
         }
-        return list.get(0);
     }
 
     @Override
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/materials/entities/MaterialCategory.java b/navalplanner-business/src/main/java/org/navalplanner/business/materials/entities/MaterialCategory.java
index e3c3d2cab..31c145096 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/materials/entities/MaterialCategory.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/materials/entities/MaterialCategory.java
@@ -229,7 +229,7 @@ public class MaterialCategory extends IntegrationEntity {
         return true;
     }
 
-    @AssertTrue
+    @AssertTrue(message = "There are repeated material category codes")
     public boolean checkConstraintNonRepeatedMaterialCategoryCodes() {
         Set<MaterialCategory> allSubcategories = getAllSubcategories();
         allSubcategories.add(this);
@@ -244,7 +244,7 @@ public class MaterialCategory extends IntegrationEntity {
         return result;
     }
 
-    @AssertTrue
+    @AssertTrue(message = "There are repeated material codes")
     public boolean checkConstraintNonRepeatedMaterialCodes() {
         Set<Material> allMaterials = getAllMaterials();
         return getFirstRepeatedCode(allMaterials) == null;