diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/ResourceCalendar.java b/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/ResourceCalendar.java
index 5d2b9aff3..53113ca6d 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/ResourceCalendar.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/calendars/entities/ResourceCalendar.java
@@ -85,7 +85,10 @@ public class ResourceCalendar extends BaseCalendar {
         return false;
     }
 
-    private Integer multiplyByCapacity(Integer workableHours) {
+    private int multiplyByCapacity(Integer workableHours) {
+        if (workableHours == null) {
+            return 0;
+        }
         if (capacity == null) {
             return workableHours;
         }