diff --git a/lib/resourceful/core.js b/lib/resourceful/core.js
index 3f57eee..eead584 100644
--- a/lib/resourceful/core.js
+++ b/lib/resourceful/core.js
@@ -116,7 +116,9 @@ resourceful.define = function (name, definition) {
 
     if (attrs) {
       Object.keys(attrs).forEach(function (k) {
-        self._properties[k] = attrs[k];
+        if (k in Factory.properties || k === '_rev') {
+          self._properties[k] = attrs[k];
+        }
       });
     }
 
diff --git a/test/hooks-sync-test.js b/test/hooks-sync-test.js
index 1c7dadd..1eb5eb7 100644
--- a/test/hooks-sync-test.js
+++ b/test/hooks-sync-test.js
@@ -7,6 +7,7 @@ vows.describe('resourceful/hooks/sync').addBatch({
     topic: function () {
       return resourceful.define('Resource', function () {
         this.property('name');
+        this.property('counter', Number);
       });
     },
     "synchronous 'before' hooks on `save`": {
@@ -41,6 +42,7 @@ vows.describe('resourceful/hooks/sync').addBatch({
     topic: function () {
       return resourceful.define('Resource2', function () {
         this.property('name');
+        this.property('counter', Number);
       });
     },
     "synchronous 'after' hooks on `save`": {
@@ -85,6 +87,7 @@ vows.describe('resourceful/hooks/sync').addBatch({
     topic: function () {
       return resourceful.define('Resource3', function () {
         this.property('title');
+        this.property('counter', Number);
       });
     },
     "with synchronous 'before' hooks on `create`": {
@@ -119,6 +122,7 @@ vows.describe('resourceful/hooks/sync').addBatch({
     topic: function () {
       return resourceful.define('Resource4', function () {
         this.property('title');
+        this.property('counter', Number);
       });
     },
     "with synchronous 'after' hooks on `create`": {
diff --git a/test/resourceful-test.js b/test/resourceful-test.js
index 80d6990..4a17990 100644
--- a/test/resourceful-test.js
+++ b/test/resourceful-test.js
@@ -138,7 +138,14 @@ vows.describe('resourceful').addVows({
         assert.include(r, 'kind');
         assert.isString(r.kind);
       }
-    }
+    }, "When instantiated with an attribute that's not a defined property": {
+        topic: function (R) {
+          return new(R)({ title: 'The Great Gatsby', kind: 'Classic Novels', author: 'F. Scott Fitzgerald' });
+        },
+        "should return `undefined` when that attribute is accessed": function(r) {
+          assert.isUndefined(r.author);
+        }
+    },
   },
   "A Resource with duplicate properties": {
     topic: function () {