diff --git a/lib/change.js b/lib/change.js
index 0aeeceb..9c0f36e 100644
--- a/lib/change.js
+++ b/lib/change.js
@@ -6,95 +6,100 @@ var Attribute = require('./attribute');
 var Protocol = require('./protocol');
 
 
-
 ///--- API
 
 function Change(options) {
   if (options) {
-    if (typeof (options) !== 'object')
-      throw new TypeError('options must be an object');
-    if (options.operation && typeof (options.operation) !== 'string')
-      throw new TypeError('options.operation must be a string');
+    assert.object(options);
+    assert.optionalString(options.operation);
   } else {
     options = {};
   }
 
-  var self = this;
   this._modification = false;
-
-  this.__defineGetter__('operation', function () {
-    switch (self._operation) {
-    case 0x00: return 'add';
-    case 0x01: return 'delete';
-    case 0x02: return 'replace';
-    default:
-      throw new Error('0x' + self._operation.toString(16) + ' is invalid');
-    }
-  });
-  this.__defineSetter__('operation', function (val) {
-    if (typeof (val) !== 'string')
-      throw new TypeError('operation must be a string');
-
-    switch (val.toLowerCase()) {
-    case 'add':
-      self._operation = 0x00;
-      break;
-    case 'delete':
-      self._operation = 0x01;
-      break;
-    case 'replace':
-      self._operation = 0x02;
-      break;
-    default:
-      throw new Error('Invalid operation type: 0x' + val.toString(16));
-    }
-  });
-  this.__defineGetter__('modification', function () {
-    return self._modification;
-  });
-  this.__defineSetter__('modification', function (attr) {
-    if (Attribute.isAttribute(attr)) {
-      self._modification = attr;
-      return;
-    }
-    // Does it have an attribute-like structure
-    if (Object.keys(attr).length == 2 &&
-        typeof (attr.type) === 'string' &&
-        Array.isArray(attr.vals)) {
-      self._modification = new Attribute({
-        type: attr.type,
-        vals: attr.vals
-      });
-      return;
-    }
-
-    var keys = Object.keys(attr);
-    if (keys.length > 1)
-      throw new Error('Only one attribute per Change allowed');
-
-    keys.forEach(function (k) {
-      var _attr = new Attribute({type: k});
-      if (Array.isArray(attr[k])) {
-        attr[k].forEach(function (v) {
-          _attr.addValue(v.toString());
-        });
-      } else {
-        _attr.addValue(attr[k].toString());
-      }
-      self._modification = _attr;
-    });
-  });
-  this.__defineGetter__('json', function () {
-    return {
-      operation: self.operation,
-      modification: self._modification ? self._modification.json : {}
-    };
-  });
-
   this.operation = options.operation || options.type || 'add';
   this.modification = options.modification || {};
 }
-module.exports = Change;
+Object.defineProperties(Change.prototype, {
+  operation: {
+    get: function getOperation() {
+      switch (this._operation) {
+      case 0x00: return 'add';
+      case 0x01: return 'delete';
+      case 0x02: return 'replace';
+      default:
+        throw new Error('0x' + this._operation.toString(16) + ' is invalid');
+      }
+    },
+    set: function setOperation(val) {
+      assert.string(val);
+      switch (val.toLowerCase()) {
+      case 'add':
+        this._operation = 0x00;
+        break;
+      case 'delete':
+        this._operation = 0x01;
+        break;
+      case 'replace':
+        this._operation = 0x02;
+        break;
+      default:
+        throw new Error('Invalid operation type: 0x' + val.toString(16));
+      }
+    },
+    configurable: false
+  },
+  modification: {
+    get: function getModification() {
+      return this._modification;
+    },
+    set: function setModification(val) {
+      if (Attribute.isAttribute(val)) {
+        this._modification = val;
+        return;
+      }
+      // Does it have an attribute-like structure
+      if (Object.keys(val).length == 2 &&
+          typeof (val.type) === 'string' &&
+          Array.isArray(val.vals)) {
+        this._modification = new Attribute({
+          type: val.type,
+          vals: val.vals
+        });
+        return;
+      }
+
+      var keys = Object.keys(val);
+      if (keys.length > 1) {
+        throw new Error('Only one attribute per Change allowed');
+      } else if (keys.length === 0) {
+        return;
+      }
+
+      var k = keys[0];
+      console.log(keys);
+      var _attr = new Attribute({type: k});
+      if (Array.isArray(val[k])) {
+        val[k].forEach(function (v) {
+          _attr.addValue(v.toString());
+        });
+      } else {
+        _attr.addValue(val[k].toString());
+      }
+      this._modification = _attr;
+    },
+    configurable: false
+  },
+  json: {
+    get: function getJSON() {
+      return {
+        operation: this.operation,
+        modification: this._modification ? this._modification.json : {}
+      };
+    },
+    configurable: false
+  }
+});
 
 Change.isChange = function isChange(change) {
   if (!change || typeof (change) !== 'object') {
@@ -206,3 +211,8 @@ Change.prototype.toBer = function (ber) {
 
   return ber;
 };
+
+
+///--- Exports
+
+module.exports = Change;
diff --git a/test/change.test.js b/test/change.test.js
index 7523b7d..a6ea7f5 100644
--- a/test/change.test.js
+++ b/test/change.test.js
@@ -32,7 +32,7 @@ test('new no args', function (t) {
 
 test('new with args', function (t) {
   var change = new Change({
-    operation: 0x00,
+    operation: 'add',
     modification: new Attribute({
       type: 'cn',
       vals: ['foo', 'bar']
@@ -50,19 +50,35 @@ test('new with args', function (t) {
 });
 
 
+test('validate fields', function (t) {
+  var c = new Change();
+  t.ok(c);
+  t.throws(function () {
+    c.operation = 'bogus';
+  });
+  t.throws(function () {
+    c.modification = {too: 'many', fields: 'here'};
+  });
+  c.modification = {
+    foo: ['bar', 'baz']
+  };
+  t.ok(c.modification);
+  t.end();
+});
+
+
 test('GH-31 (multiple attributes per Change)', function (t) {
-  try {
-    t.notOk(new Change({
+  t.throws(function () {
+    var c = new Change({
       operation: 'replace',
       modification: {
         cn: 'foo',
         sn: 'bar'
       }
-    }), 'should have thrown');
-  } catch (e) {
-    t.ok(e);
-    t.end();
-  }
+    });
+    t.notOk(c);
+  });
+  t.end();
 });