--- a/testing/marionette/message.js
+++ b/testing/marionette/message.js
@@ -44,20 +44,20 @@ class Message {
    *
    * @throws {TypeError}
    *     If the message type is not recognised.
    */
   static fromPacket(data) {
     const [type] = data;
 
     switch (type) {
-      case Command.TYPE:
+      case Command.Type:
         return Command.fromPacket(data);
 
-      case Response.TYPE:
+      case Response.Type:
         return Response.fromPacket(data);
 
       default:
         throw new TypeError(
             "Unrecognised message type in packet: " + JSON.stringify(data));
     }
   }
 }
@@ -152,17 +152,17 @@ class Command extends Message {
   /**
    * Encodes the command to a packet.
    *
    * @return {Array}
    *     Packet.
    */
   toPacket() {
     return [
-      Command.TYPE,
+      Command.Type,
       this.id,
       this.name,
       this.parameters,
     ];
   }
 
   /**
    * Converts a data packet into {@link Command}.
@@ -174,27 +174,27 @@ class Command extends Message {
    * @return {Command}
    *     Representation of packet.
    *
    * @throws {TypeError}
    *     If the message type is not recognised.
    */
   static fromPacket(payload) {
     let [type, msgID, name, params] = payload;
-    assert.that(n => n === Command.TYPE)(type);
+    assert.that(n => n === Command.Type)(type);
 
     // if parameters are given but null, treat them as undefined
     if (params === null) {
       params = undefined;
     }
 
     return new Command(msgID, name, params);
   }
 }
-Command.TYPE = 0;
+Command.Type = 0;
 
 const validator = {
   exclusionary: {
     "capabilities": ["error", "value"],
     "error": ["value", "sessionId", "capabilities"],
     "sessionId": ["error", "value"],
     "value": ["error", "sessionId", "capabilities"],
   },
@@ -321,17 +321,17 @@ class Response extends Message {
   /**
    * Encodes the response to a packet.
    *
    * @return {Array}
    *     Packet.
    */
   toPacket() {
     return [
-      Response.TYPE,
+      Response.Type,
       this.id,
       this.error,
       this.body,
     ];
   }
 
   /**
    * Converts a data packet into {@link Response}.
@@ -343,22 +343,22 @@ class Response extends Message {
    * @return {Response}
    *     Representation of packet.
    *
    * @throws {TypeError}
    *     If the message type is not recognised.
    */
   static fromPacket(payload) {
     let [type, msgID, err, body] = payload;
-    assert.that(n => n === Response.TYPE)(type);
+    assert.that(n => n === Response.Type)(type);
 
     let resp = new Response(msgID);
     resp.error = assert.string(err);
 
     resp.body = body;
     return resp;
   }
 }
-Response.TYPE = 1;
+Response.Type = 1;
 
 this.Message = Message;
 this.Command = Command;
 this.Response = Response;

--- a/testing/marionette/test_message.js
+++ b/testing/marionette/test_message.js
@@ -63,17 +63,17 @@ add_test(function test_Command_onrespons
 
   run_next_test();
 });
 
 add_test(function test_Command_ctor() {
   let cmd = new Command(42, "bar", {bar: "baz"});
   let msg = cmd.toPacket();
 
-  equal(Command.TYPE, msg[0]);
+  equal(Command.Type, msg[0]);
   equal(cmd.id, msg[1]);
   equal(cmd.name, msg[2]);
   equal(cmd.parameters, msg[3]);
 
   run_next_test();
 });
 
 add_test(function test_Command_toString() {
@@ -100,18 +100,18 @@ add_test(function test_Command_fromPacke
   Assert.throws(() => Command.fromPacket([0, 2, "foo", false]));
 
   let nullParams = Command.fromPacket([0, 2, "foo", null]);
   equal("[object Object]", Object.prototype.toString.call(nullParams.parameters));
 
   run_next_test();
 });
 
-add_test(function test_Command_TYPE() {
-  equal(0, Command.TYPE);
+add_test(function test_Command_Type() {
+  equal(0, Command.Type);
   run_next_test();
 });
 
 add_test(function test_Response_ctor() {
   let handler = () => run_next_test();
 
   let resp = new Response(42, handler);
   equal(42, resp.id);
@@ -195,17 +195,17 @@ add_test(function test_Response_sendErro
 
   run_next_test();
 });
 
 add_test(function test_Response_toPacket() {
   let resp = new Response(42, () => {});
   let msg = resp.toPacket();
 
-  equal(Response.TYPE, msg[0]);
+  equal(Response.Type, msg[0]);
   equal(resp.id, msg[1]);
   equal(resp.error, msg[2]);
   equal(resp.body, msg[3]);
 
   run_next_test();
 });
 
 add_test(function test_Response_toString() {
@@ -234,12 +234,12 @@ add_test(function test_Response_fromPack
   Assert.throws(() => Response.fromPacket([0, 2, "foo", {}]));
   Assert.throws(() => Response.fromPacket([1, null, "foo", {}]));
   Assert.throws(() => Response.fromPacket([1, 2, null, {}]));
   Response.fromPacket([1, 2, "foo", null]);
 
   run_next_test();
 });
 
-add_test(function test_Response_TYPE() {
-  equal(1, Response.TYPE);
+add_test(function test_Response_Type() {
+  equal(1, Response.Type);
   run_next_test();
 });