diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/MachineWorkersConfigurationUnit.java b/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/MachineWorkersConfigurationUnit.java
index d2d5d8019..4367838b4 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/MachineWorkersConfigurationUnit.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/MachineWorkersConfigurationUnit.java
@@ -27,6 +27,7 @@ import java.util.HashSet;
 import java.util.Set;
 
 import org.hibernate.validator.AssertTrue;
+import org.hibernate.validator.Valid;
 import org.navalplanner.business.common.BaseEntity;
 
 /**
@@ -75,6 +76,7 @@ public class MachineWorkersConfigurationUnit extends BaseEntity {
         this.alpha = alpha;
     }
 
+    @Valid
     public BigDecimal getAlpha() {
         return alpha;
     }
@@ -159,6 +161,11 @@ public class MachineWorkersConfigurationUnit extends BaseEntity {
         return assigned;
     }
 
+    @AssertTrue(message = "Alpha must be greater than 0")
+    public boolean checkAlpha() {
+        return (this.alpha.compareTo(new BigDecimal(0)) > 0);
+    }
+
     @AssertTrue(message = "All Machine worker assignments must have a start date earlier than the finish date")
     public boolean checkWorkerAssignmentsIntervalsProperlyDefined() {
         boolean correctIntervals = true;
diff --git a/navalplanner-webapp/src/main/webapp/resources/machine/_editMachine.zul b/navalplanner-webapp/src/main/webapp/resources/machine/_editMachine.zul
index 60e452dd6..9b0f67e49 100644
--- a/navalplanner-webapp/src/main/webapp/resources/machine/_editMachine.zul
+++ b/navalplanner-webapp/src/main/webapp/resources/machine/_editMachine.zul
@@ -40,17 +40,17 @@
                         <row>
                             <label value="${i18n:_('Code')}" />
                             <textbox value="@{controller.machine.code}" width="500px"
-                                constraint="no empty:${i18n:_('cannot be null or empty')}" />
+                                constraint="no empty:${i18n:_('Code cannot be null or empty')}" />
                         </row>
                         <row>
                             <label value="${i18n:_('Name')}" />
                             <textbox value="@{controller.machine.name}" width="500px"
-                                constraint="no empty:${i18n:_('cannot be null or empty')}" />
+                                constraint="no empty:${i18n:_('Name cannot be null or empty')}" />
                         </row>
                         <row>
                             <label value="${i18n:_('Description')}" />
                             <textbox value="@{controller.machine.description}" width="500px"
-                                constraint="no empty:${i18n:_('cannot be null or empty')}" />
+                                constraint="no empty:${i18n:_('Description cannot be null or empty')}" />
                         </row>
                     </rows>
                 </grid>
diff --git a/navalplanner-webapp/src/main/webapp/resources/machine/_machineConfigurationUnits.zul b/navalplanner-webapp/src/main/webapp/resources/machine/_machineConfigurationUnits.zul
index c09a740aa..1236c9e41 100644
--- a/navalplanner-webapp/src/main/webapp/resources/machine/_machineConfigurationUnits.zul
+++ b/navalplanner-webapp/src/main/webapp/resources/machine/_machineConfigurationUnits.zul
@@ -127,7 +127,7 @@
                 <textbox value="@{configurationUnit.name}"
                     constraint="no empty:${i18n:_('cannot be null or empty')}" />
                 <textbox value="@{configurationUnit.alpha}"
-                    constraint="no negative,no zero,no empty:${i18n:_('cannot be null or empty')}" />
+                    constraint="no zero,no empty,/[1-9][0-9]*(\.[0-9][0-9]?)?/:${i18n:_('must be a real positive number')}" />
                 <button sclass="icono" image="/common/img/ico_borrar1.png"
                     hoverImage="/common/img/ico_borrar.png" tooltiptext="${i18n:_('Delete')}"
                     onClick="configurationController.deleteConfigurationUnit(self.parent.value)">