diff --git a/core/src/main/java/io/github/sebastiantoepfer/jsonschema/core/vocab/core/VocabularyKeywordType.java b/core/src/main/java/io/github/sebastiantoepfer/jsonschema/core/vocab/core/VocabularyKeywordType.java
index 92177c7f..764ae661 100644
--- a/core/src/main/java/io/github/sebastiantoepfer/jsonschema/core/vocab/core/VocabularyKeywordType.java
+++ b/core/src/main/java/io/github/sebastiantoepfer/jsonschema/core/vocab/core/VocabularyKeywordType.java
@@ -25,6 +25,7 @@
 
 import io.github.sebastiantoepfer.jsonschema.InstanceType;
 import io.github.sebastiantoepfer.jsonschema.JsonSchema;
+import io.github.sebastiantoepfer.jsonschema.keyword.Identifier;
 import io.github.sebastiantoepfer.jsonschema.keyword.Keyword;
 import io.github.sebastiantoepfer.jsonschema.keyword.KeywordType;
 import io.github.sebastiantoepfer.jsonschema.vocabulary.spi.VocabularyDefinition;
@@ -32,8 +33,6 @@
 import jakarta.json.JsonObject;
 import jakarta.json.JsonValue;
 import java.net.URI;
-import java.util.Collection;
-import java.util.List;
 import java.util.Objects;
 import java.util.stream.Stream;
 
@@ -62,7 +61,7 @@ public Keyword createKeyword(final JsonSchema schema, final JsonValue value) {
         return result;
     }
 
-    public final class VocabularyKeyword implements Keyword, VocabularyDefinitions {
+    public final class VocabularyKeyword implements Identifier, VocabularyDefinitions {
 
         private final JsonObject vocabularies;
 
@@ -75,8 +74,8 @@ public final class VocabularyKeyword implements Keyword, VocabularyDefinitions {
         }
 
         @Override
-        public Collection<KeywordCategory> categories() {
-            return List.of();
+        public URI asUri() {
+            return definitions().map(VocabularyDefinition::id).findFirst().orElseThrow();
         }
 
         @Override