diff --git a/src/ConstArray.js b/src/ConstArray.js
index 89a08da..e73faca 100644
--- a/src/ConstArray.js
+++ b/src/ConstArray.js
@@ -11,7 +11,7 @@ import {
 export function ConstArray(size) {
   const obj = { _size: size }
   Object.setPrototypeOf(obj, ConstArray.prototype)
-  obj.new(ConstArray, arguments)
+  obj.new('ConstArray', arguments)
   return obj
 }
 ConstArray.prototype.serialize = function (dv, src, ...inner_types) {
diff --git a/src/ConstDataView.js b/src/ConstDataView.js
index ef32ce2..42721d8 100644
--- a/src/ConstDataView.js
+++ b/src/ConstDataView.js
@@ -3,7 +3,7 @@ import { memcpy, Type } from '.'
 export function ConstDataView(size) {
   const obj = { _size: size }
   Object.setPrototypeOf(obj, ConstDataView.prototype)
-  obj.new(ConstDataView, arguments)
+  obj.new('ConstDataView', arguments)
   return obj
 }
 ConstDataView.prototype.serialize = function (dv, src) {
diff --git a/src/ConstString.js b/src/ConstString.js
index 164cc72..69e1537 100644
--- a/src/ConstString.js
+++ b/src/ConstString.js
@@ -4,7 +4,7 @@ import { Type } from './Type'
 export function ConstString(size) {
   const obj = { _size: size }
   Object.setPrototypeOf(obj, ConstString.prototype)
-  obj.new(ConstString, arguments)
+  obj.new('ConstString', arguments)
   return obj
 }
 ConstString.prototype.serialize = function (dv, src) {
diff --git a/src/Int.js b/src/Int.js
index 83428b5..fb981ab 100644
--- a/src/Int.js
+++ b/src/Int.js
@@ -3,7 +3,7 @@ import { Type, limits } from '.'
 export function Int(bits, sign) {
   const obj = { _size: bits / 8 }
   Object.setPrototypeOf(obj, Int.prototype)
-  obj.new(Int, arguments)
+  obj.new('Int', arguments)
 
   switch (sign) {
     case 'signed':
diff --git a/src/Sequence.js b/src/Sequence.js
index 98c3a16..969fa1d 100644
--- a/src/Sequence.js
+++ b/src/Sequence.js
@@ -4,7 +4,7 @@ import { Type } from './Type'
 export function Sequence(types) {
   const obj = { _types: types, _headless: false, _sizeof: 0 }
   Object.setPrototypeOf(obj, Sequence.prototype)
-  obj.new(Sequence, [
+  obj.new('Sequence', [
     types.map((arg) => {
       if (typeof arg == 'function') {
         return arg.name
diff --git a/src/Struct.js b/src/Struct.js
index 1a89d03..75224f5 100644
--- a/src/Struct.js
+++ b/src/Struct.js
@@ -37,7 +37,7 @@ export function Struct(type_obj) {
   }
 
   obj._size = offset
-  obj.new(Struct, [arg])
+  obj.new('Struct', [arg])
 
   return obj
 }
@@ -47,6 +47,9 @@ Struct.prototype.serialize = function (dv, src) {
   for (const [key, value] of Object.entries(src)) {
     const info = this._info_by_key.get(key)
 
+    if (info == undefined) {
+      throw new Error(this._name + " doesn't have key " + key)
+    }
     if (info.headless) {
       dv.setUint32(info.offset, data_offset)
       const frame = new DataView(dv.buffer, dv.byteOffset + data_offset)
@@ -80,7 +83,7 @@ Struct.prototype.isHeadless = function () {
 Struct.prototype.sizeof = function (arg) {
   if (this._headless) {
     if (arg === undefined) {
-      throw new Error('unknown size of ' + this)
+      throw new Error('unknown size of ' + this._name)
     }
     let size = this._size
 
diff --git a/src/Type.js b/src/Type.js
index 97331a9..b30d554 100644
--- a/src/Type.js
+++ b/src/Type.js
@@ -3,8 +3,8 @@ export function Type() {
   Object.setPrototypeOf(obj, Type.prototype)
   return obj
 }
-Type.prototype.new = function (func, args) {
-  this._name = func.name
+Type.prototype.new = function (name, args) {
+  this._name = name
   if (args !== undefined) {
     const str_args = Array.from(args).map((arg) => {
       if (typeof arg == 'function') {
diff --git a/test/Struct.test.js b/test/Struct.test.js
index d93973a..761a5fb 100644
--- a/test/Struct.test.js
+++ b/test/Struct.test.js
@@ -40,6 +40,8 @@ describe(Struct.name, () => {
     const dv = sizedDataView(sizeof(Vector2))
     expect(16).toEqual(dv.byteLength)
 
+    expect(() => serialize(dv, { x: 1, z: 2 }, Vector2)).toThrow()
+
     serialize(dv, vector2, Vector2)
     expectDataViewEqual(dv, vector2_dv)
   })