diff --git a/src/main/java/com/coveo/pushapiclient/Document.java b/src/main/java/com/coveo/pushapiclient/Document.java
index 22fa35b4..cc94e3d3 100644
--- a/src/main/java/com/coveo/pushapiclient/Document.java
+++ b/src/main/java/com/coveo/pushapiclient/Document.java
@@ -1,8 +1,26 @@
 package com.coveo.pushapiclient;
 
-import java.util.Map;
+import java.util.HashMap;
 
 public class Document {
+    /**
+     * The metadata key-value pairs for a given document.
+     * <p>
+     * Each metadata in the document must be unique.
+     * <p>
+     * Metadata are case-insensitive (e.g., the Push API considers mykey, MyKey, myKey, MYKEY, etc. as identical).
+     * <p>
+     * See https://docs.coveo.com/en/115 for more information.
+     */
+    public final HashMap<String, Object> metadata;
+    /**
+     * The list of permission sets for this item.
+     * <p>
+     * This is useful when item based security is required (i.e., when security isn't configured at the source level).
+     * <p>
+     * See https://docs.coveo.com/en/107 for more information.
+     */
+    public final DocumentPermissions[] permissions;
     /**
      * The Uniform Resource Identifier (URI) that uniquely identifies the document in a Coveo index.
      * <p>
@@ -73,24 +91,6 @@ public class Document {
      * See https://docs.coveo.com/en/73 for more information.
      */
     public CompressedBinaryData compressedBinaryData;
-    /**
-     * The metadata key-value pairs for a given document.
-     * <p>
-     * Each metadata in the document must be unique.
-     * <p>
-     * Metadata are case-insensitive (e.g., the Push API considers mykey, MyKey, myKey, MYKEY, etc. as identical).
-     * <p>
-     * See https://docs.coveo.com/en/115 for more information.
-     */
-    public Map<String, Object> metadata;
-    /**
-     * The list of permission sets for this item.
-     * <p>
-     * This is useful when item based security is required (i.e., when security isn't configured at the source level).
-     * <p>
-     * See https://docs.coveo.com/en/107 for more information.
-     */
-    public DocumentPermissions[] permissions;
     /**
      * The file extension of the data you're pushing.
      * <p>
@@ -104,6 +104,7 @@ public class Document {
 
     public Document() {
         this.permissions = new DocumentPermissions[]{new DocumentPermissions()};
+        this.metadata = new HashMap<String, Object>();
     }
 }
 
diff --git a/src/main/java/com/coveo/pushapiclient/DocumentBuilder.java b/src/main/java/com/coveo/pushapiclient/DocumentBuilder.java
index e7a7ce96..edda89ab 100644
--- a/src/main/java/com/coveo/pushapiclient/DocumentBuilder.java
+++ b/src/main/java/com/coveo/pushapiclient/DocumentBuilder.java
@@ -1,14 +1,28 @@
 package com.coveo.pushapiclient;
 
 import com.google.gson.Gson;
+import com.google.gson.JsonObject;
 import org.joda.time.DateTime;
 import org.joda.time.format.ISODateTimeFormat;
 
+import java.util.ArrayList;
 import java.util.Date;
 import java.util.Map;
 
 public class DocumentBuilder {
-    private Document document;
+
+    private static final ArrayList<String> reservedKeynames = new ArrayList<>() {{
+        add("compressedBinaryData");
+        add("compressedBinaryDataFileId");
+        add("parentId");
+        add("fileExtension");
+        add("data");
+        add("permissions");
+        add("documentId");
+        add("orderingId");
+    }};
+
+    private final Document document;
 
     public DocumentBuilder(String uri, String title) {
         this.document = new Document();
@@ -133,7 +147,13 @@ public DocumentBuilder withDeniedPermissions() {
     }
 
     public String marshal() {
-        return new Gson().toJson(this.document);
+        JsonObject jsonDocument = new Gson().toJsonTree(this.document).getAsJsonObject();
+        this.document.metadata.forEach((key, value) -> {
+            jsonDocument.add(key, new Gson().toJsonTree(value));
+        });
+        jsonDocument.remove("metadata");
+        return jsonDocument.toString();
+
     }
 
     private String dateFormat(DateTime dt) {
@@ -154,6 +174,8 @@ private void validateFileExtension(String fileExtension) {
     }
 
     private void validateReservedMetadataKeyNames(String key) {
-        // TODO
+        if (reservedKeynames.contains(key)) {
+            throw new RuntimeException(String.format("Cannot use %s as a metadata key: It is a reserved keynames. See https://docs.coveo.com/en/78/index-content/push-api-reference#json-document-reserved-key-names", key));
+        }
     }
 }
diff --git a/src/main/java/com/coveo/testlocally/TestingLocally.java b/src/main/java/com/coveo/testlocally/TestingLocally.java
index 650f0582..afdb857d 100644
--- a/src/main/java/com/coveo/testlocally/TestingLocally.java
+++ b/src/main/java/com/coveo/testlocally/TestingLocally.java
@@ -28,13 +28,21 @@ public static void main(String[] args) {
 
     public static void testPushDocument(String sourceId, Source source) {
         DocumentBuilder doc = new DocumentBuilder("https://perdu.com", "the title").withData("this is searchable").withDate(new Date());
+        DocumentBuilder docWithMetadata = new DocumentBuilder("https://perdu.com/3", "the title 3").withMetadata(new HashMap<>() {{
+            put("foo", "bar");
+            put("my_field_1", "1");
+            put("my_field_2", false);
+            put("my_field_3", 1234);
+            put("my_field_4", new String[]{"a", "b", "c"});
+        }});
         System.out.println(doc.marshal());
+        System.out.println(docWithMetadata.marshal());
         try {
             source.addOrUpdateDocument(sourceId, doc);
+            source.addOrUpdateDocument(sourceId, docWithMetadata);
         } catch (IOException | InterruptedException e) {
             System.out.println(e);
         }
-
     }
 
     public static void testManageIdentities(Source source) {