diff --git a/addon/src/main/java/org/vaadin/stefan/fullcalendar/Entry.java b/addon/src/main/java/org/vaadin/stefan/fullcalendar/Entry.java
index 211f450b..7b3c31db 100644
--- a/addon/src/main/java/org/vaadin/stefan/fullcalendar/Entry.java
+++ b/addon/src/main/java/org/vaadin/stefan/fullcalendar/Entry.java
@@ -98,6 +98,7 @@ public class Entry {
 
     private Set<String> classNames;
 
+    @JsonName("extendedProps")
     private Map<String, Object> customProperties;
 
     @JsonIgnore