diff --git a/libreplan-business/src/main/resources/org/libreplan/business/resources/entities/Resources.hbm.xml b/libreplan-business/src/main/resources/org/libreplan/business/resources/entities/Resources.hbm.xml
index 6498b0ab2..f701410f1 100644
--- a/libreplan-business/src/main/resources/org/libreplan/business/resources/entities/Resources.hbm.xml
+++ b/libreplan-business/src/main/resources/org/libreplan/business/resources/entities/Resources.hbm.xml
@@ -118,7 +118,7 @@
         column="predefined_criterion_internal_name" />
     <property access="field" name="active"/>
     <many-to-one access="field" name="type" lazy="false" column="id_criterion_type" not-null="true" />
-    <many-to-one access="field" name="costCategory" lazy="false" column="id_cost_category" not-null="true" />
+    <many-to-one access="field" name="costCategory" lazy="false" column="id_cost_category" not-null="false" />
 
     <!--  Indexed. It is probable to navigate from a criterion
     to its children criteria -->