diff --git a/navalplanner-webapp/src/main/java/org/navalplanner/web/planner/allocation/AllocationRow.java b/navalplanner-webapp/src/main/java/org/navalplanner/web/planner/allocation/AllocationRow.java
index 577a94718..b2db5bed6 100644
--- a/navalplanner-webapp/src/main/java/org/navalplanner/web/planner/allocation/AllocationRow.java
+++ b/navalplanner-webapp/src/main/java/org/navalplanner/web/planner/allocation/AllocationRow.java
@@ -244,7 +244,7 @@ public abstract class AllocationRow {
         if (origin != null) {
             return origin.getAssignedHours();
         }
-        return null;
+        return 0;
     }
 
     public void applyDisabledRules(CalculatedValue calculatedValue) {
@@ -258,4 +258,8 @@ public abstract class AllocationRow {
         hoursInput.setValue(last.getAssignedHours());
         resourcesPerDayInput.setValue(last.getResourcesPerDay().getAmount());
     }
+
+    public void addListenerForHoursInputChange(EventListener listener) {
+        hoursInput.addEventListener(Events.ON_CHANGE, listener);
+    }
 }
diff --git a/navalplanner-webapp/src/main/java/org/navalplanner/web/planner/allocation/FormBinder.java b/navalplanner-webapp/src/main/java/org/navalplanner/web/planner/allocation/FormBinder.java
index f9a9dc75b..691de7f3c 100644
--- a/navalplanner-webapp/src/main/java/org/navalplanner/web/planner/allocation/FormBinder.java
+++ b/navalplanner-webapp/src/main/java/org/navalplanner/web/planner/allocation/FormBinder.java
@@ -105,6 +105,16 @@ class FormBinder {
 
     private EventListener recommendedCheckboxListener;
 
+    private EventListener hoursInputChange = new EventListener() {
+
+        @Override
+        public void onEvent(Event event) throws Exception {
+            if (assignedHoursComponent.isDisabled()) {
+                assignedHoursComponent.setValue(sumAllHoursFromHoursInputs());
+            }
+        }
+    };
+
     public FormBinder(
             AllocationRowsHandler allocationRowsHandler,
             IResourceAllocationModel resourceAllocationModel) {
@@ -163,6 +173,20 @@ class FormBinder {
         }
     }
 
+    private void bindTotalHoursToHoursInputs() {
+        for (AllocationRow each : rows) {
+            each.addListenerForHoursInputChange(hoursInputChange);
+        }
+    }
+
+    private int sumAllHoursFromHoursInputs() {
+        int result = 0;
+        for (AllocationRow each : rows) {
+            result += each.getHoursFromInput();
+        }
+        return result;
+    }
+
     public CalculatedValue getCalculatedValue() {
         return allocationRowsHandler.getCalculatedValue();
     }
@@ -221,6 +245,7 @@ class FormBinder {
                 .getCurrentRows());
         rows = result;
         applyDisabledRulesOnRows();
+        bindTotalHoursToHoursInputs();
         return result;
     }