diff --git a/Schema.js b/Schema.js
index b0ea4d81..3f590ac7 100644
--- a/Schema.js
+++ b/Schema.js
@@ -100,9 +100,6 @@ function fieldNameIsValidForClass(fieldName, className) {
 }
 
 function invalidClassNameMessage(className) {
-  if (!className) {
-    className = '';
-  }
   return 'Invalid classname: ' + className + ', classnames can only have alphanumeric characters and _, and must start with an alpha character ';
 }
 
@@ -137,7 +134,7 @@ function schemaAPITypeToMongoFieldType(type) {
     return { error: "invalid JSON", code: Parse.Error.INVALID_JSON };
   }
   switch (type.type) {
-    default:         return { error: 'invalid field type: ' + type.type };
+    default:         return { error: 'invalid field type: ' + type.type, code: Parse.Error.INCORRECT_TYPE };
     case 'Number':   return { result: 'number' };
     case 'String':   return { result: 'string' };
     case 'Boolean':  return { result: 'boolean' };
@@ -211,10 +208,10 @@ Schema.prototype.reload = function() {
 // enabled) before calling this function.
 Schema.prototype.addClassIfNotExists = function(className, fields) {
   if (this.data[className]) {
-    return Promise.reject(new Parse.Error(
-      Parse.Error.DUPLICATE_VALUE,
-      'class ' + className + ' already exists'
-    ));
+    return Promise.reject({
+      code: Parse.Error.INVALID_CLASS_NAME,
+      error: 'class ' + className + ' already exists',
+    });
   }
 
   if (!classNameIsValid(className)) {
@@ -222,9 +219,6 @@ Schema.prototype.addClassIfNotExists = function(className, fields) {
       code: Parse.Error.INVALID_CLASS_NAME,
       error: invalidClassNameMessage(className),
     });
-    return Promise.reject({
-      code: Parse.Error.INVALID_CLASS_NAME,
-    });
   }
   for (fieldName in fields) {
     if (!fieldNameIsValid(fieldName)) {
diff --git a/spec/Schema.spec.js b/spec/Schema.spec.js
index ce6f5968..a9cd6271 100644
--- a/spec/Schema.spec.js
+++ b/spec/Schema.spec.js
@@ -155,9 +155,11 @@ describe('Schema', () => {
     .then(schema => {
       schema.validateObject('NewClass', {foo: 7})
       .then(() => {
-        schema.addClassIfNotExists('NewClass', {
+        schema.reload()
+        .then(schema => schema.addClassIfNotExists('NewClass', {
           foo: {type: 'String'}
-        }).catch(error => {
+        }))
+        .catch(error => {
           expect(error.code).toEqual(Parse.Error.INVALID_CLASS_NAME)
           expect(error.error).toEqual('class NewClass already exists');
           done();
@@ -223,7 +225,17 @@ describe('Schema', () => {
     });
   });
 
-  it('refuses to explicitly create the default fields', done => {
+  it('refuses to explicitly create the default fields for custom classes', done => {
+    config.database.loadSchema()
+    .then(schema => schema.addClassIfNotExists('NewClass', {objectId: {type: 'String'}}))
+    .catch(error => {
+      expect(error.code).toEqual(136);
+      expect(error.error).toEqual('field objectId cannot be added');
+      done();
+    });
+  });
+
+  it('refuses to explicitly create the default fields for non-custom classes', done => {
     config.database.loadSchema()
     .then(schema => schema.addClassIfNotExists('_Installation', {localeIdentifier: {type: 'String'}}))
     .catch(error => {
@@ -317,6 +329,18 @@ describe('Schema', () => {
     });
   });
 
+  it('refuses to add fields with unknown types', done => {
+    config.database.loadSchema()
+    .then(schema => schema.addClassIfNotExists('NewClass', {
+      foo: {type: 'Unknown'},
+    }))
+    .catch(error => {
+      expect(error.code).toEqual(Parse.Error.INCORRECT_TYPE);
+      expect(error.error).toEqual('invalid field type: Unknown');
+      done();
+    });
+  });
+
   it('will create classes', done => {
     config.database.loadSchema()
     .then(schema => schema.addClassIfNotExists('NewClass', {
@@ -352,6 +376,32 @@ describe('Schema', () => {
     });
   });
 
+  it('creates the default fields for non-custom classes', done => {
+    config.database.loadSchema()
+    .then(schema => schema.addClassIfNotExists('_Installation', {
+      foo: {type: 'Number'},
+    }))
+    .then(mongoObj => {
+      expect(mongoObj).toEqual({
+        _id: '_Installation',
+        createdAt: 'string',
+        updatedAt: 'string',
+        objectId: 'string',
+        foo: 'number',
+        installationId: 'string',
+        deviceToken: 'string',
+        channels: 'array',
+        deviceType: 'string',
+        pushType: 'string',
+        GCMSenderId: 'string',
+        timeZone: 'string',
+        localeIdentifier: 'string',
+        badge: 'number',
+      });
+      done();
+    });
+  });
+
   it('refuses to create two geopoints', done => {
     config.database.loadSchema()
     .then(schema => schema.addClassIfNotExists('NewClass', {