diff --git a/src/main/java/org/springframework/hateoas/alps/Ext.java b/src/main/java/org/springframework/hateoas/alps/Ext.java
index 91e83782..ed31ad27 100644
--- a/src/main/java/org/springframework/hateoas/alps/Ext.java
+++ b/src/main/java/org/springframework/hateoas/alps/Ext.java
@@ -29,6 +29,7 @@ import lombok.Value;
 @Builder
 public class Ext {
 
+	private final String id;
 	private final String href;
 	private final String value;
 }
diff --git a/src/test/java/org/springframework/hateoas/alps/JacksonSerializationTest.java b/src/test/java/org/springframework/hateoas/alps/JacksonSerializationTest.java
index 44e47a92..3609852a 100644
--- a/src/test/java/org/springframework/hateoas/alps/JacksonSerializationTest.java
+++ b/src/test/java/org/springframework/hateoas/alps/JacksonSerializationTest.java
@@ -66,7 +66,7 @@ public class JacksonSerializationTest {
 								).build(), //
 						descriptor().id("resultType").type(Type.SEMANTIC).//
 								doc(doc().value("results format").build()).//
-								ext(ext().href("http://alps.io/ext/range").value("summary,detail").build()//
+								ext(ext().id("#ext-range").href("http://alps.io/ext/range").value("summary,detail").build()//
 								).build())//
 				).build();
 
diff --git a/src/test/resources/org/springframework/hateoas/alps/reference.json b/src/test/resources/org/springframework/hateoas/alps/reference.json
index 24b2d066..c68937b0 100644
--- a/src/test/resources/org/springframework/hateoas/alps/reference.json
+++ b/src/test/resources/org/springframework/hateoas/alps/reference.json
@@ -24,6 +24,7 @@
     },
     "type" : "SEMANTIC",
     "ext" : {
+      "id" : "#ext-range",
       "href" : "http://alps.io/ext/range",
       "value" : "summary,detail"
     }