diff --git a/navalplanner-webapp/src/main/java/org/navalplanner/web/materials/IMaterialsModel.java b/navalplanner-webapp/src/main/java/org/navalplanner/web/materials/IMaterialsModel.java
index c5bdce961..8002cbd0d 100644
--- a/navalplanner-webapp/src/main/java/org/navalplanner/web/materials/IMaterialsModel.java
+++ b/navalplanner-webapp/src/main/java/org/navalplanner/web/materials/IMaterialsModel.java
@@ -36,7 +36,7 @@ import org.zkoss.ganttz.util.MutableTreeModel;
  */
 public interface IMaterialsModel {
 
-    void addMaterialCategory(MaterialCategory parent, MaterialCategory child) throws ValidationException;
+    void addMaterialCategory(MaterialCategory parent, String categoryName) throws ValidationException;
 
     void addMaterialToMaterialCategory(MaterialCategory materialCategory);
 
diff --git a/navalplanner-webapp/src/main/java/org/navalplanner/web/materials/MaterialsController.java b/navalplanner-webapp/src/main/java/org/navalplanner/web/materials/MaterialsController.java
index a8421e599..e73769229 100644
--- a/navalplanner-webapp/src/main/java/org/navalplanner/web/materials/MaterialsController.java
+++ b/navalplanner-webapp/src/main/java/org/navalplanner/web/materials/MaterialsController.java
@@ -248,14 +248,13 @@ public class MaterialsController extends
             throw new WrongValueException(txtCategory, _("cannot be null or empty"));
         }
 
-        final MaterialCategory category = MaterialCategory.create(_(categoryName));
         MaterialCategory parent = null;
         final Treeitem treeitem = categoriesTree.getSelectedItem();
         if (treeitem != null) {
             parent = (MaterialCategory) treeitem.getValue();
         }
         try {
-            materialsModel.addMaterialCategory(parent, category);
+            materialsModel.addMaterialCategory(parent, categoryName);
             txtCategory.setValue("");
             reloadCategoriesTree(treeitem);
         } catch (ValidationException e) {
diff --git a/navalplanner-webapp/src/main/java/org/navalplanner/web/materials/MaterialsModel.java b/navalplanner-webapp/src/main/java/org/navalplanner/web/materials/MaterialsModel.java
index 6323a6e21..5ef16e579 100644
--- a/navalplanner-webapp/src/main/java/org/navalplanner/web/materials/MaterialsModel.java
+++ b/navalplanner-webapp/src/main/java/org/navalplanner/web/materials/MaterialsModel.java
@@ -121,8 +121,10 @@ public class MaterialsModel implements IMaterialsModel {
     }
 
     @Override
-    public void addMaterialCategory(MaterialCategory parent, MaterialCategory child) throws ValidationException {
-        Validate.notNull(child);
+    public void addMaterialCategory(MaterialCategory parent, String categoryName) throws ValidationException {
+        Validate.notNull(categoryName);
+
+        MaterialCategory child = MaterialCategory.create(_(categoryName));
 
         final MaterialCategory materialCategory = findMaterialCategory(child);
         if (materialCategory != null) {