diff --git a/package.json b/package.json
index f4fa93616..99e63d889 100644
--- a/package.json
+++ b/package.json
@@ -1,11 +1,11 @@
 {
 	"private": true,
 	"dependencies": {
-		"lerna": "^2.4.0",
+		"cross-env": "^5.1.1",
 		"husky": "^0.13.4",
-		"prettier": "^1.4.4",
+		"lerna": "^2.4.0",
 		"lint-staged": "^3.6.1",
-		"cross-env":"^5.1.1"
+		"prettier": "^1.4.4"
 	},
 	"scripts": {
 		"clean": "lerna clean",
diff --git a/packages/mobx-state-tree/package.json b/packages/mobx-state-tree/package.json
index 390b23a0a..e044c79f7 100644
--- a/packages/mobx-state-tree/package.json
+++ b/packages/mobx-state-tree/package.json
@@ -55,7 +55,7 @@
     "tape": "^4.6.0",
     "tslib": "^1.7.1",
     "tslint": "^3.15.1",
-    "typescript": "^2.4.2"
+    "typescript": "^2.7.1"
   },
   "peerDependencies": {
     "mobx": "^3.1.15"
diff --git a/packages/mobx-state-tree/src/types/complex-types/model.ts b/packages/mobx-state-tree/src/types/complex-types/model.ts
index 2b35decff..f4ec55e3f 100644
--- a/packages/mobx-state-tree/src/types/complex-types/model.ts
+++ b/packages/mobx-state-tree/src/types/complex-types/model.ts
@@ -191,7 +191,7 @@ export class ModelType<S, T> extends ComplexType<S, T> implements IModelType<S,
 
     props<SP, TP>(
         properties: { [K in keyof TP]: IType<any, TP[K]> } & { [K in keyof SP]: IType<SP[K], any> }
-    ): IModelType<S & SP, T & TP> {
+    ): IModelType<S & SP & Snapshot<SP>, T & TP> {
         return this.cloneAndEnhance({ properties } as any)
     }
 
@@ -457,7 +457,7 @@ export interface IModelType<S, T> extends IComplexType<S, T & IStateTreeNode> {
         props: { [K in keyof TP]: IType<any, TP[K]> | TP[K] } &
             { [K in keyof SP]: IType<SP[K], any> | SP[K] }
     ): IModelType<S & Snapshot<SP>, T & TP>
-    //props<P>(props: IModelProperties<P>): IModelType<S & Snapshot<P>, T & P>
+    props<P>(props: IModelProperties<P>): IModelType<S & Snapshot<P>, T & P>
     views<V extends Object>(fn: (self: T & IStateTreeNode) => V): IModelType<S, T & V>
     actions<A extends { [name: string]: Function }>(
         fn: (self: T & IStateTreeNode) => A
@@ -480,11 +480,12 @@ export type Snapshot<T> = {
     [K in keyof T]?: Snapshot<T[K]> | any // Any because we cannot express conditional types yet, so this escape is needed for refs and such....
 }
 
+export function model<T = {}>(): IModelType<T | Snapshot<T>, T>
+export function model<T = {}>(properties: IModelProperties<T>): IModelType<Snapshot<T>, T>
 export function model<T = {}>(
     name: string,
-    properties?: IModelProperties<T>
-): IModelType<Snapshot<T>, T>
-export function model<T = {}>(properties?: IModelProperties<T>): IModelType<Snapshot<T>, T>
+    properties: IModelProperties<T>
+): IModelType<T | Snapshot<T>, T>
 /**
  * Creates a new model type by providing a name, properties, volatile state and actions.
  *
@@ -493,10 +494,11 @@ export function model<T = {}>(properties?: IModelProperties<T>): IModelType<Snap
  * @export
  * @alias types.model
  */
-export function model(...args: any[]) {
-    const name = typeof args[0] === "string" ? args.shift() : "AnonymousModel"
+export function model<T = {}>(...args: any[]): IModelType<Snapshot<any>, any> {
+    const name = typeof args[0] === "string" ? args.shift() as string : "AnonymousModel"
     const properties = args.shift() || {}
-    return new ModelType({ name, properties })
+    const config = { name: name as string, properties } as ModelTypeConfig
+    return new ModelType(config)
 }
 
 export function compose<T1, S1, T2, S2, T3, S3>(
diff --git a/packages/mobx-state-tree/src/utils.ts b/packages/mobx-state-tree/src/utils.ts
index 723a0bb63..f4f9607a9 100644
--- a/packages/mobx-state-tree/src/utils.ts
+++ b/packages/mobx-state-tree/src/utils.ts
@@ -51,8 +51,8 @@ export function extendKeepGetter(a: any, ...b: any[]) {
     for (let i = 0; i < b.length; i++) {
         const current = b[i]
         for (let key in current) {
-            const descriptor = Object.getOwnPropertyDescriptor(current, key)
-            if ("get" in descriptor) {
+            const descriptor = Object.getOwnPropertyDescriptor(current, key) || {}
+            if (descriptor && "get" in descriptor) {
                 Object.defineProperty(a, key, { ...descriptor, configurable: true })
                 continue
             }
diff --git a/yarn.lock b/yarn.lock
index 52ac8ca5e..3858db96d 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -10503,6 +10503,10 @@ typescript@^2.4.2:
   version "2.5.3"
   resolved "https://registry.yarnpkg.com/typescript/-/typescript-2.5.3.tgz#df3dcdc38f3beb800d4bc322646b04a3f6ca7f0d"
 
+typescript@^2.7.1:
+  version "2.7.1"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-2.7.1.tgz#bb3682c2c791ac90e7c6210b26478a8da085c359"
+
 ua-parser-js@^0.7.9:
   version "0.7.17"
   resolved "https://registry.yarnpkg.com/ua-parser-js/-/ua-parser-js-0.7.17.tgz#e9ec5f9498b9ec910e7ae3ac626a805c4d09ecac"