diff --git a/lib/bson/binary.js b/lib/bson/binary.js
index 6d190bca..58f41dde 100644
--- a/lib/bson/binary.js
+++ b/lib/bson/binary.js
@@ -40,8 +40,6 @@ function Binary(buffer, subType) {
     throw new Error('only String, Buffer, Uint8Array or Array accepted');
   }
 
-  this._bsontype = 'Binary';
-
   if (buffer instanceof Number) {
     this.sub_type = buffer;
     this.position = 0;
@@ -81,6 +79,11 @@ function Binary(buffer, subType) {
   }
 }
 
+Object.defineProperty(Binary.prototype, '_bsontype', {
+  value: 'Binary',
+  writable: false
+});
+
 /**
  * Updates this binary with byte_value.
  *
diff --git a/lib/bson/code.js b/lib/bson/code.js
index c2984cd5..ec333da0 100644
--- a/lib/bson/code.js
+++ b/lib/bson/code.js
@@ -8,11 +8,15 @@
  */
 var Code = function Code(code, scope) {
   if (!(this instanceof Code)) return new Code(code, scope);
-  this._bsontype = 'Code';
   this.code = code;
   this.scope = scope;
 };
 
+Object.defineProperty(Code.prototype, '_bsontype', {
+  value: 'Code',
+  writable: false
+});
+
 /**
  * @ignore
  */
diff --git a/lib/bson/db_ref.js b/lib/bson/db_ref.js
index f95795b1..342c4c96 100644
--- a/lib/bson/db_ref.js
+++ b/lib/bson/db_ref.js
@@ -10,12 +10,16 @@
 function DBRef(namespace, oid, db) {
   if (!(this instanceof DBRef)) return new DBRef(namespace, oid, db);
 
-  this._bsontype = 'DBRef';
   this.namespace = namespace;
   this.oid = oid;
   this.db = db;
 }
 
+Object.defineProperty(DBRef.prototype, '_bsontype', {
+  value: 'DBRef',
+  writable: false
+});
+
 /**
  * @ignore
  * @api private
diff --git a/lib/bson/decimal128.js b/lib/bson/decimal128.js
index 924513f4..ab82b8a9 100644
--- a/lib/bson/decimal128.js
+++ b/lib/bson/decimal128.js
@@ -181,10 +181,14 @@ var lessThan = function(left, right) {
  * @return {Double}
  */
 var Decimal128 = function(bytes) {
-  this._bsontype = 'Decimal128';
   this.bytes = bytes;
 };
 
+Object.defineProperty(Decimal128.prototype, '_bsontype', {
+  value: 'Decimal128',
+  writable: false
+});
+
 /**
  * Create a Decimal128 instance from a string representation
  *
diff --git a/lib/bson/double.js b/lib/bson/double.js
index 523c21f8..ca529c2a 100644
--- a/lib/bson/double.js
+++ b/lib/bson/double.js
@@ -8,10 +8,14 @@
 function Double(value) {
   if (!(this instanceof Double)) return new Double(value);
 
-  this._bsontype = 'Double';
   this.value = value;
 }
 
+Object.defineProperty(Double.prototype, '_bsontype', {
+  value: 'Double',
+  writable: false
+});
+
 /**
  * Access the number value.
  *
diff --git a/lib/bson/int_32.js b/lib/bson/int_32.js
index 85dbdec6..93e0cc61 100644
--- a/lib/bson/int_32.js
+++ b/lib/bson/int_32.js
@@ -8,10 +8,14 @@
 var Int32 = function(value) {
   if (!(this instanceof Int32)) return new Int32(value);
 
-  this._bsontype = 'Int32';
   this.value = value;
 };
 
+Object.defineProperty(Int32.prototype, '_bsontype', {
+  value: 'Int32',
+  writable: false
+});
+
 /**
  * Access the number value.
  *
diff --git a/lib/bson/long.js b/lib/bson/long.js
index 78215aa3..7f473ba8 100644
--- a/lib/bson/long.js
+++ b/lib/bson/long.js
@@ -43,7 +43,6 @@
 function Long(low, high) {
   if (!(this instanceof Long)) return new Long(low, high);
 
-  this._bsontype = 'Long';
   /**
    * @type {number}
    * @ignore
@@ -57,6 +56,11 @@ function Long(low, high) {
   this.high_ = high | 0; // force into 32 signed bits.
 }
 
+Object.defineProperty(Long.prototype, '_bsontype', {
+  value: 'Long',
+  writable: false
+});
+
 /**
  * Return the int value.
  *
diff --git a/lib/bson/max_key.js b/lib/bson/max_key.js
index eebca7bc..1fa7f536 100644
--- a/lib/bson/max_key.js
+++ b/lib/bson/max_key.js
@@ -6,9 +6,12 @@
  */
 function MaxKey() {
   if (!(this instanceof MaxKey)) return new MaxKey();
-
-  this._bsontype = 'MaxKey';
 }
 
+Object.defineProperty(MaxKey.prototype, '_bsontype', {
+  value: 'MaxKey',
+  writable: false
+});
+
 module.exports = MaxKey;
 module.exports.MaxKey = MaxKey;
diff --git a/lib/bson/min_key.js b/lib/bson/min_key.js
index 15f45228..6bcacd1e 100644
--- a/lib/bson/min_key.js
+++ b/lib/bson/min_key.js
@@ -6,9 +6,12 @@
  */
 function MinKey() {
   if (!(this instanceof MinKey)) return new MinKey();
-
-  this._bsontype = 'MinKey';
 }
 
+Object.defineProperty(MinKey.prototype, '_bsontype', {
+  value: 'MinKey',
+  writable: false
+});
+
 module.exports = MinKey;
 module.exports.MinKey = MinKey;
diff --git a/lib/bson/objectid.js b/lib/bson/objectid.js
index 79de40d2..3c437536 100644
--- a/lib/bson/objectid.js
+++ b/lib/bson/objectid.js
@@ -39,8 +39,6 @@ var ObjectID = function ObjectID(id) {
   if (id instanceof ObjectID) return id;
   if (!(this instanceof ObjectID)) return new ObjectID(id);
 
-  this._bsontype = 'ObjectID';
-
   // The most common usecase (blank id, new objectId instance)
   if (id == null || typeof id === 'number') {
     // Generate a new id
@@ -78,6 +76,11 @@ var ObjectID = function ObjectID(id) {
   if (ObjectID.cacheHexString) this.__id = this.toString('hex');
 };
 
+Object.defineProperty(ObjectID.prototype, '_bsontype', {
+  value: 'ObjectID',
+  writable: false
+});
+
 // Allow usage of ObjectId as well as ObjectID
 // var ObjectId = ObjectID;
 
diff --git a/lib/bson/parser/calculate_size.js b/lib/bson/parser/calculate_size.js
index 7e0026ca..96aebd6d 100644
--- a/lib/bson/parser/calculate_size.js
+++ b/lib/bson/parser/calculate_size.js
@@ -61,6 +61,7 @@ function calculateElement(name, value, serializeFunctions, isArray, ignoreUndefi
   if (value && value.toBSON) {
     value = value.toBSON();
   }
+  var _bsontype, _objPrototype;
 
   switch (typeof value) {
     case 'string':
@@ -84,15 +85,17 @@ function calculateElement(name, value, serializeFunctions, isArray, ignoreUndefi
     case 'boolean':
       return (name != null ? Buffer.byteLength(name, 'utf8') + 1 : 0) + (1 + 1);
     case 'object':
+      var _objPrototype = value && Object.getPrototypeOf(value)
+      var _bsontype = _objPrototype && _objPrototype._bsontype || undefined;
       if (
         value == null ||
         value instanceof MinKey ||
         value instanceof MaxKey ||
-        value['_bsontype'] === 'MinKey' ||
-        value['_bsontype'] === 'MaxKey'
+        _bsontype === 'MinKey' ||
+        _bsontype === 'MaxKey'
       ) {
         return (name != null ? Buffer.byteLength(name, 'utf8') + 1 : 0) + 1;
-      } else if (value instanceof ObjectID || value['_bsontype'] === 'ObjectID' || value['_bsontype'] === 'ObjectId') {
+      } else if (value instanceof ObjectID || _bsontype === 'ObjectID' || _bsontype === 'ObjectId') {
         return (name != null ? Buffer.byteLength(name, 'utf8') + 1 : 0) + (12 + 1);
       } else if (value instanceof Date || isDate(value)) {
         return (name != null ? Buffer.byteLength(name, 'utf8') + 1 : 0) + (8 + 1);
@@ -104,14 +107,14 @@ function calculateElement(name, value, serializeFunctions, isArray, ignoreUndefi
         value instanceof Long ||
         value instanceof Double ||
         value instanceof Timestamp ||
-        value['_bsontype'] === 'Long' ||
-        value['_bsontype'] === 'Double' ||
-        value['_bsontype'] === 'Timestamp'
+        _bsontype === 'Long' ||
+        _bsontype === 'Double' ||
+        _bsontype === 'Timestamp'
       ) {
         return (name != null ? Buffer.byteLength(name, 'utf8') + 1 : 0) + (8 + 1);
-      } else if (value instanceof Decimal128 || value['_bsontype'] === 'Decimal128') {
+      } else if (value instanceof Decimal128 || _bsontype === 'Decimal128') {
         return (name != null ? Buffer.byteLength(name, 'utf8') + 1 : 0) + (16 + 1);
-      } else if (value instanceof Code || value['_bsontype'] === 'Code') {
+      } else if (value instanceof Code || _bsontype === 'Code') {
         // Calculate size depending on the availability of a scope
         if (value.scope != null && Object.keys(value.scope).length > 0) {
           return (
@@ -132,7 +135,7 @@ function calculateElement(name, value, serializeFunctions, isArray, ignoreUndefi
             1
           );
         }
-      } else if (value instanceof Binary || value['_bsontype'] === 'Binary') {
+      } else if (value instanceof Binary || _bsontype === 'Binary') {
         // Check what kind of subtype we have
         if (value.sub_type === Binary.SUBTYPE_BYTE_ARRAY) {
           return (
@@ -144,7 +147,7 @@ function calculateElement(name, value, serializeFunctions, isArray, ignoreUndefi
             (name != null ? Buffer.byteLength(name, 'utf8') + 1 : 0) + (value.position + 1 + 4 + 1)
           );
         }
-      } else if (value instanceof Symbol || value['_bsontype'] === 'Symbol') {
+      } else if (value instanceof Symbol || _bsontype === 'Symbol') {
         return (
           (name != null ? Buffer.byteLength(name, 'utf8') + 1 : 0) +
           Buffer.byteLength(value.value, 'utf8') +
@@ -152,7 +155,7 @@ function calculateElement(name, value, serializeFunctions, isArray, ignoreUndefi
           1 +
           1
         );
-      } else if (value instanceof DBRef || value['_bsontype'] === 'DBRef') {
+      } else if (value instanceof DBRef || _bsontype === 'DBRef') {
         // Set up correct object for serialization
         var ordered_values = {
           $ref: value.namespace,
@@ -183,7 +186,7 @@ function calculateElement(name, value, serializeFunctions, isArray, ignoreUndefi
           (value.multiline ? 1 : 0) +
           1
         );
-      } else if (value instanceof BSONRegExp || value['_bsontype'] === 'BSONRegExp') {
+      } else if (value instanceof BSONRegExp || _bsontype === 'BSONRegExp') {
         return (
           (name != null ? Buffer.byteLength(name, 'utf8') + 1 : 0) +
           1 +
diff --git a/lib/bson/parser/serializer.js b/lib/bson/parser/serializer.js
index e4ff2bd9..803b6867 100644
--- a/lib/bson/parser/serializer.js
+++ b/lib/bson/parser/serializer.js
@@ -705,6 +705,9 @@ var serializeInto = function serializeInto(
       }
 
       var type = typeof value;
+      var _objPrototype = value && type === 'object' && Object.getPrototypeOf(value)
+      var _bsontype = _objPrototype && _objPrototype._bsontype || undefined;
+
       if (type === 'string') {
         index = serializeString(buffer, key, value, index, true);
       } else if (type === 'number') {
@@ -717,13 +720,13 @@ var serializeInto = function serializeInto(
         index = serializeNull(buffer, key, value, index, true);
       } else if (value === null) {
         index = serializeNull(buffer, key, value, index, true);
-      } else if (value['_bsontype'] === 'ObjectID' || value['_bsontype'] === 'ObjectId') {
+      } else if (_bsontype === 'ObjectID' || _bsontype === 'ObjectId') {
         index = serializeObjectId(buffer, key, value, index, true);
       } else if (Buffer.isBuffer(value)) {
         index = serializeBuffer(buffer, key, value, index, true);
       } else if (value instanceof RegExp || isRegExp(value)) {
         index = serializeRegExp(buffer, key, value, index, true);
-      } else if (type === 'object' && value['_bsontype'] == null) {
+      } else if (type === 'object' && _bsontype == null) {
         index = serializeObject(
           buffer,
           key,
@@ -736,11 +739,11 @@ var serializeInto = function serializeInto(
           true,
           path
         );
-      } else if (type === 'object' && value['_bsontype'] === 'Decimal128') {
+      } else if (type === 'object' && _bsontype === 'Decimal128') {
         index = serializeDecimal128(buffer, key, value, index, true);
-      } else if (value['_bsontype'] === 'Long' || value['_bsontype'] === 'Timestamp') {
+      } else if (_bsontype === 'Long' || _bsontype === 'Timestamp') {
         index = serializeLong(buffer, key, value, index, true);
-      } else if (value['_bsontype'] === 'Double') {
+      } else if (_bsontype === 'Double') {
         index = serializeDouble(buffer, key, value, index, true);
       } else if (typeof value === 'function' && serializeFunctions) {
         index = serializeFunction(
@@ -753,7 +756,7 @@ var serializeInto = function serializeInto(
           serializeFunctions,
           true
         );
-      } else if (value['_bsontype'] === 'Code') {
+      } else if (_bsontype === 'Code') {
         index = serializeCode(
           buffer,
           key,
@@ -765,18 +768,20 @@ var serializeInto = function serializeInto(
           ignoreUndefined,
           true
         );
-      } else if (value['_bsontype'] === 'Binary') {
+      } else if (_bsontype === 'Binary') {
         index = serializeBinary(buffer, key, value, index, true);
-      } else if (value['_bsontype'] === 'Symbol') {
+      } else if (_bsontype === 'Symbol') {
         index = serializeSymbol(buffer, key, value, index, true);
-      } else if (value['_bsontype'] === 'DBRef') {
+      } else if (_bsontype === 'DBRef') {
         index = serializeDBRef(buffer, key, value, index, depth, serializeFunctions, true);
-      } else if (value['_bsontype'] === 'BSONRegExp') {
+      } else if (_bsontype === 'BSONRegExp') {
         index = serializeBSONRegExp(buffer, key, value, index, true);
-      } else if (value['_bsontype'] === 'Int32') {
+      } else if (_bsontype === 'Int32') {
         index = serializeInt32(buffer, key, value, index, true);
-      } else if (value['_bsontype'] === 'MinKey' || value['_bsontype'] === 'MaxKey') {
+      } else if (_bsontype === 'MinKey' || _bsontype === 'MaxKey') {
         index = serializeMinMax(buffer, key, value, index, true);
+      } else if (typeof value['_bsontype'] !== 'undefined') {
+        throw new TypeError('Unrecognized or invalid _bsontype: ' + value['_bsontype']);
       }
     }
   } else if (object instanceof Map) {
@@ -797,6 +802,9 @@ var serializeInto = function serializeInto(
       // Check the type of the value
       type = typeof value;
 
+      var _objPrototype = value && type === 'object' && Object.getPrototypeOf(value)
+      var _bsontype = _objPrototype && _objPrototype._bsontype || undefined;
+
       // Check the key and throw error if it's illegal
       if (typeof key === 'string' && ignoreKeys.indexOf(key) === -1) {
         if (key.match(regexp) != null) {
@@ -825,13 +833,13 @@ var serializeInto = function serializeInto(
         // } else if (value === undefined && ignoreUndefined === true) {
       } else if (value === null || (value === undefined && ignoreUndefined === false)) {
         index = serializeNull(buffer, key, value, index);
-      } else if (value['_bsontype'] === 'ObjectID' || value['_bsontype'] === 'ObjectId') {
+      } else if (_bsontype === 'ObjectID' || _bsontype === 'ObjectId') {
         index = serializeObjectId(buffer, key, value, index);
       } else if (Buffer.isBuffer(value)) {
         index = serializeBuffer(buffer, key, value, index);
       } else if (value instanceof RegExp || isRegExp(value)) {
         index = serializeRegExp(buffer, key, value, index);
-      } else if (type === 'object' && value['_bsontype'] == null) {
+      } else if (type === 'object' && _bsontype == null) {
         index = serializeObject(
           buffer,
           key,
@@ -844,13 +852,13 @@ var serializeInto = function serializeInto(
           false,
           path
         );
-      } else if (type === 'object' && value['_bsontype'] === 'Decimal128') {
+      } else if (type === 'object' && _bsontype === 'Decimal128') {
         index = serializeDecimal128(buffer, key, value, index);
-      } else if (value['_bsontype'] === 'Long' || value['_bsontype'] === 'Timestamp') {
+      } else if (_bsontype === 'Long' || _bsontype === 'Timestamp') {
         index = serializeLong(buffer, key, value, index);
-      } else if (value['_bsontype'] === 'Double') {
+      } else if (_bsontype === 'Double') {
         index = serializeDouble(buffer, key, value, index);
-      } else if (value['_bsontype'] === 'Code') {
+      } else if (_bsontype === 'Code') {
         index = serializeCode(
           buffer,
           key,
@@ -863,18 +871,20 @@ var serializeInto = function serializeInto(
         );
       } else if (typeof value === 'function' && serializeFunctions) {
         index = serializeFunction(buffer, key, value, index, checkKeys, depth, serializeFunctions);
-      } else if (value['_bsontype'] === 'Binary') {
+      } else if (_bsontype === 'Binary') {
         index = serializeBinary(buffer, key, value, index);
-      } else if (value['_bsontype'] === 'Symbol') {
+      } else if (_bsontype === 'Symbol') {
         index = serializeSymbol(buffer, key, value, index);
-      } else if (value['_bsontype'] === 'DBRef') {
+      } else if (_bsontype === 'DBRef') {
         index = serializeDBRef(buffer, key, value, index, depth, serializeFunctions);
-      } else if (value['_bsontype'] === 'BSONRegExp') {
+      } else if (_bsontype === 'BSONRegExp') {
         index = serializeBSONRegExp(buffer, key, value, index);
-      } else if (value['_bsontype'] === 'Int32') {
+      } else if (_bsontype === 'Int32') {
         index = serializeInt32(buffer, key, value, index);
-      } else if (value['_bsontype'] === 'MinKey' || value['_bsontype'] === 'MaxKey') {
+      } else if (_bsontype === 'MinKey' || _bsontype === 'MaxKey') {
         index = serializeMinMax(buffer, key, value, index);
+      } else if (typeof value['_bsontype'] !== 'undefined') {
+        throw new TypeError('Unrecognized or invalid _bsontype: ' + value['_bsontype']);
       }
     }
   } else {
@@ -898,6 +908,9 @@ var serializeInto = function serializeInto(
       // Check the type of the value
       type = typeof value;
 
+      var _objPrototype = value && type === 'object' && Object.getPrototypeOf(value)
+      var _bsontype = _objPrototype && _objPrototype._bsontype || undefined;
+
       // Check the key and throw error if it's illegal
       if (typeof key === 'string' && ignoreKeys.indexOf(key) === -1) {
         if (key.match(regexp) != null) {
@@ -927,13 +940,13 @@ var serializeInto = function serializeInto(
         if (ignoreUndefined === false) index = serializeNull(buffer, key, value, index);
       } else if (value === null) {
         index = serializeNull(buffer, key, value, index);
-      } else if (value['_bsontype'] === 'ObjectID' || value['_bsontype'] === 'ObjectId') {
+      } else if (_bsontype === 'ObjectID' || _bsontype === 'ObjectId') {
         index = serializeObjectId(buffer, key, value, index);
       } else if (Buffer.isBuffer(value)) {
         index = serializeBuffer(buffer, key, value, index);
       } else if (value instanceof RegExp || isRegExp(value)) {
         index = serializeRegExp(buffer, key, value, index);
-      } else if (type === 'object' && value['_bsontype'] == null) {
+      } else if (type === 'object' && _bsontype == null) {
         index = serializeObject(
           buffer,
           key,
@@ -946,13 +959,13 @@ var serializeInto = function serializeInto(
           false,
           path
         );
-      } else if (type === 'object' && value['_bsontype'] === 'Decimal128') {
+      } else if (type === 'object' && _bsontype === 'Decimal128') {
         index = serializeDecimal128(buffer, key, value, index);
-      } else if (value['_bsontype'] === 'Long' || value['_bsontype'] === 'Timestamp') {
+      } else if (_bsontype === 'Long' || _bsontype === 'Timestamp') {
         index = serializeLong(buffer, key, value, index);
-      } else if (value['_bsontype'] === 'Double') {
+      } else if (_bsontype === 'Double') {
         index = serializeDouble(buffer, key, value, index);
-      } else if (value['_bsontype'] === 'Code') {
+      } else if (_bsontype === 'Code') {
         index = serializeCode(
           buffer,
           key,
@@ -965,18 +978,20 @@ var serializeInto = function serializeInto(
         );
       } else if (typeof value === 'function' && serializeFunctions) {
         index = serializeFunction(buffer, key, value, index, checkKeys, depth, serializeFunctions);
-      } else if (value['_bsontype'] === 'Binary') {
+      } else if (_bsontype === 'Binary') {
         index = serializeBinary(buffer, key, value, index);
-      } else if (value['_bsontype'] === 'Symbol') {
+      } else if (_bsontype === 'Symbol') {
         index = serializeSymbol(buffer, key, value, index);
-      } else if (value['_bsontype'] === 'DBRef') {
+      } else if (_bsontype === 'DBRef') {
         index = serializeDBRef(buffer, key, value, index, depth, serializeFunctions);
-      } else if (value['_bsontype'] === 'BSONRegExp') {
+      } else if (_bsontype === 'BSONRegExp') {
         index = serializeBSONRegExp(buffer, key, value, index);
-      } else if (value['_bsontype'] === 'Int32') {
+      } else if (_bsontype === 'Int32') {
         index = serializeInt32(buffer, key, value, index);
-      } else if (value['_bsontype'] === 'MinKey' || value['_bsontype'] === 'MaxKey') {
+      } else if (_bsontype === 'MinKey' || _bsontype === 'MaxKey') {
         index = serializeMinMax(buffer, key, value, index);
+      } else if (typeof value['_bsontype'] !== 'undefined') {
+        throw new TypeError('Unrecognized or invalid _bsontype: ' + value['_bsontype']);
       }
     }
   }
diff --git a/lib/bson/regexp.js b/lib/bson/regexp.js
index 108f0166..8a4b18e6 100644
--- a/lib/bson/regexp.js
+++ b/lib/bson/regexp.js
@@ -8,7 +8,6 @@ function BSONRegExp(pattern, options) {
   if (!(this instanceof BSONRegExp)) return new BSONRegExp();
 
   // Execute
-  this._bsontype = 'BSONRegExp';
   this.pattern = pattern || '';
   this.options = options || '';
 
@@ -29,5 +28,10 @@ function BSONRegExp(pattern, options) {
   }
 }
 
+Object.defineProperty(BSONRegExp.prototype, '_bsontype', {
+  value: 'BSONRegExp',
+  writable: false
+});
+
 module.exports = BSONRegExp;
 module.exports.BSONRegExp = BSONRegExp;
diff --git a/lib/bson/symbol.js b/lib/bson/symbol.js
index ba20cabe..f0ba5af4 100644
--- a/lib/bson/symbol.js
+++ b/lib/bson/symbol.js
@@ -11,10 +11,14 @@ var inspect = Buffer ? require('util').inspect.custom || 'inspect' : 'inspect';
  */
 function Symbol(value) {
   if (!(this instanceof Symbol)) return new Symbol(value);
-  this._bsontype = 'Symbol';
   this.value = value;
 }
 
+Object.defineProperty(Symbol.prototype, '_bsontype', {
+  value: 'Symbol',
+  writable: false
+});
+
 /**
  * Access the wrapped string value.
  *
diff --git a/lib/bson/timestamp.js b/lib/bson/timestamp.js
index dc61a6cc..3c711715 100644
--- a/lib/bson/timestamp.js
+++ b/lib/bson/timestamp.js
@@ -44,7 +44,6 @@
  */
 function Timestamp(low, high) {
   if (!(this instanceof Timestamp)) return new Timestamp(low, high);
-  this._bsontype = 'Timestamp';
   /**
    * @type {number}
    * @ignore
@@ -58,6 +57,11 @@ function Timestamp(low, high) {
   this.high_ = high | 0; // force into 32 signed bits.
 }
 
+Object.defineProperty(Timestamp.prototype, '_bsontype', {
+  value: 'Timestamp',
+  writable: false
+});
+
 /**
  * Return the int value.
  *
diff --git a/test/node/bsontype_test.js b/test/node/bsontype_test.js
new file mode 100644
index 00000000..80ef7f90
--- /dev/null
+++ b/test/node/bsontype_test.js
@@ -0,0 +1,102 @@
+'use strict';
+
+var createBSON = require('../utils');
+var M = require('../../lib/bson/map');
+
+function testSerializeAndDeserialize(test, expected) {
+  var result;
+  test.doesNotThrow(function() {
+    var bson = createBSON();
+    result = bson.deserialize(bson.serialize(expected));
+  });
+  test.deepEqual(result, expected);
+}
+
+exports['Should throw on an unknown _bsontype'] = function(test) {
+  function myBsonType () {
+    this.x = 12;
+  }
+  myBsonType.prototype._bsontype = 'myBsonType';
+
+  test.throws(function() {
+    createBSON().serialize({ a: new myBsonType() });
+  });
+  test.done();
+}
+
+exports['Should ignore _bsontype that is not on the prototype'] = function(test) {
+  testSerializeAndDeserialize(test, { a: { _bsontype: 'foo' } });
+  test.done();
+}
+
+exports['Should be able to handle serializing null and Object.create(null)'] = function(test) {
+  testSerializeAndDeserialize(test, {
+    a: null,
+    b: Object.create(null)
+  });
+  test.done();
+}
+
+exports['Should throw on an unknown _bsontype in an array'] = function(test) {
+  function myBsonType () {
+    this.x = 12;
+  }
+  myBsonType.prototype._bsontype = 'myBsonType';
+
+  test.throws(function() {
+    createBSON().serialize({ a: [ new myBsonType() ] });
+  });
+  test.done();
+}
+
+exports['Should ingore _bsontype that is not on the prototype in an array'] = function(test) {
+  testSerializeAndDeserialize(test, { a: [{ _bsontype: 'foo' }] });
+  test.done();
+}
+
+exports['Should be able to handle serializing null and Object.create(null) in an array'] = function(test) {
+  testSerializeAndDeserialize(test, {
+    a: [
+      null,
+      Object.create(null)
+    ]
+  });
+  test.done();
+}
+
+exports['Should throw on an unknown _bsontype in a Map'] = function(test) {
+  function myBsonType () {
+    this.x = 12;
+  }
+  myBsonType.prototype._bsontype = 'myBsonType';
+
+  test.throws(function() {
+    createBSON().serialize({ a: new M([ ['x', new myBsonType()] ]) });
+  });
+  test.done();
+}
+
+exports['Should ingore _bsontype that is not on the prototype in a Map'] = function(test) {
+  var result;
+  test.doesNotThrow(function() {
+    var bson = createBSON();
+    result = bson.deserialize(bson.serialize({ a: new M([[ '_bsontype', 'foo' ]]) }));
+  });
+  test.deepEqual(result, { a: { _bsontype: 'foo' } });
+  test.done();
+}
+
+exports['Should be able to handle serializing null and Object.create(null) in a Map'] = function(test) {
+  var result;
+  test.doesNotThrow(function() {
+    var bson = createBSON();
+    result = bson.deserialize(bson.serialize({
+      a: new M([
+        ['a', null],
+        ['b', Object.create(null)]
+      ])
+    }));
+  });
+  test.deepEqual(result, { a: { a: null, b: {} } });
+  test.done();
+}