diff --git a/src/Definition.php b/src/Definition.php
index 5041154..a9c0849 100644
--- a/src/Definition.php
+++ b/src/Definition.php
@@ -25,13 +25,6 @@
  */
 class Definition
 {
-    /**
-     * The model group.
-     *
-     * @var string|null
-     */
-    protected $group;
-
     /**
      * The model class name.
      *
@@ -40,11 +33,11 @@ class Definition
     protected $class;
 
     /**
-     * The full model name.
+     * The model group.
      *
-     * @var string
+     * @var string|null
      */
-    protected $model;
+    protected $group;
 
     /**
      * The closure callback.
@@ -63,50 +56,47 @@ class Definition
     /**
      * Create a new model definition.
      *
-     * @param string $model The full model name.
+     * @param string $class The model class name.
      *
      * @return void
      */
-    public function __construct($model)
+    public function __construct($class)
     {
-        if (strpos($model, ':') !== false) {
-            $this->group = current(explode(':', $model));
-            $this->class = str_replace($this->group.':', '', $model);
-        } else {
-            $this->class = $model;
-        }
-
-        $this->model = $model;
+        $this->class = $class;
     }
 
     /**
-     * Get the definition group.
+     * Returns the real model class without the group prefix.
      *
-     * @return string|null
+     * @return string
      */
-    public function getGroup()
+    public function getClass()
     {
-        return $this->group;
+        return $this->class;
     }
 
     /**
-     * Returns the real model class without the group prefix.
+     * Set the model group.
      *
-     * @return string
+     * @param string|null $group
+     *
+     * @return $this
      */
-    public function getClass()
+    public function setGroup($group)
     {
-        return $this->class;
+        $this->group = $group;
+
+        return $this;
     }
 
     /**
-     * Get the full model name including group prefixes.
+     * Get the model group.
      *
-     * @return string
+     * @return string|null
      */
-    public function getModel()
+    public function getGroup()
     {
-        return $this->model;
+        return $this->group;
     }
 
     /**
diff --git a/src/FactoryMuffin.php b/src/FactoryMuffin.php
index a6400e9..670f560 100644
--- a/src/FactoryMuffin.php
+++ b/src/FactoryMuffin.php
@@ -215,13 +215,11 @@ protected function make($model, array $attr, $save)
             Arr::add($this->pending, $object);
         }
 
-        // Get the group specific attribute definitions
-        if ($definition->getGroup()) {
-            $attr = array_merge($attr, $this->getDefinition($model)->getDefinitions());
-        }
+        // Get the attribute definitions
+        $attributes = array_merge($this->getDefinition($model)->getDefinitions(), $attr);
 
         // Generate and save each attribute for the model
-        $this->generate($object, $attr);
+        $this->generate($object, $attributes);
 
         return $object;
     }
@@ -408,11 +406,8 @@ public function instance($model, array $attr = [])
      */
     protected function generate($object, array $attr = [])
     {
-        $definitions = $this->getDefinition(get_class($object))->getDefinitions();
-        $attributes = array_merge($definitions, $attr);
-
         // Generate and save each attribute
-        foreach ($attributes as $key => $kind) {
+        foreach ($attr as $key => $kind) {
             $generated = $this->getGeneratorFactory()->generate($kind, $object);
             $this->setAttribute($object, $key, $generated);
         }
@@ -445,7 +440,16 @@ public function getDefinition($model)
      */
     public function define($model)
     {
-        return $this->definitions[$model] = new Definition($model);
+        if (strpos($model, ':') !== false) {
+            $group = current(explode(':', $model));
+            $class = str_replace($group.':', '', $model);
+            $this->definitions[$model] = clone $this->getDefinition($class);
+            $this->definitions[$model]->setGroup($group);
+        } else {
+            $this->definitions[$model] = new Definition($model);
+        }
+
+        return $this->definitions[$model];
     }
 
     /**
diff --git a/tests/DefinitionTest.php b/tests/DefinitionTest.php
index c08bad6..01a7ed1 100644
--- a/tests/DefinitionTest.php
+++ b/tests/DefinitionTest.php
@@ -44,7 +44,6 @@ public function testBasicDefinitionFunctions()
 
         $this->assertNull($definition->getGroup());
         $this->assertSame('AttributeDefinitionsStub', $definition->getClass());
-        $this->assertSame('AttributeDefinitionsStub', $definition->getModel());
     }
 
     public function testAttributeDefinitionFunctions()
@@ -93,6 +92,7 @@ public function testDefineWithReplacementGenerators()
         ]);
 
         $this->assertInstanceOf('UserModelStub', $user);
+        $this->assertSame('foo', $user->test);
         $this->assertInternalType('string', $user->name);
         $this->assertInternalType('string', $user->fullName);
         $this->assertNotEquals('name', $user->fullName);
@@ -119,6 +119,7 @@ public function testGroupDefine()
         $user = static::$fm->create('group:UserModelStub');
 
         $this->assertInstanceOf('UserModelStub', $user);
+        $this->assertSame('foo', $user->test);
         $this->assertInternalType('string', $user->address);
         $this->assertNotEquals('address', $user->address);
         $this->assertInternalType('string', $user->name);
@@ -131,12 +132,21 @@ public function testGroupDefineOverwrite()
         $user = static::$fm->create('anothergroup:UserModelStub');
 
         $this->assertInstanceOf('UserModelStub', $user);
+        $this->assertSame('foo', $user->test);
         $this->assertInternalType('string', $user->address);
         $this->assertInternalType('string', $user->name);
         $this->assertSame('custom', $user->active);
         $this->assertContains('@', $user->email);
     }
 
+    public function testGroupKeepCallback()
+    {
+        $user = static::$fm->create('UserModelStub');
+
+        $this->assertInstanceOf('UserModelStub', $user);
+        $this->assertSame('foo', $user->test);
+    }
+
     public function testGroupCallback()
     {
         $user = static::$fm->create('callbackgroup:UserModelStub');
@@ -148,6 +158,17 @@ public function testGroupCallback()
         $this->assertContains('@', $user->email);
     }
 
+    public function testGroupClearAttributes()
+    {
+        $user = static::$fm->create('noattributes:UserModelStub');
+
+        $this->assertInstanceOf('UserModelStub', $user);
+        $this->assertSame('foo', $user->test);
+        $this->assertFalse(isset($user->name));
+        $this->assertFalse(isset($user->active));
+        $this->assertFalse(isset($user->email));
+    }
+
     /**
      * @expectedException \League\FactoryMuffin\Exceptions\NoDefinedFactoryException
      */
@@ -168,7 +189,10 @@ public function testShouldThrowExceptionWhenLoadingANonExistentGroup()
     public function testGroupDefineNoBaseModel()
     {
         try {
-            static::$fm->create('foo:DogModelStub');
+            static::$fm->define('foo:DogModelStub')->setDefinitions([
+                'name' => Faker::firstNameMale(),
+                'age'  => Faker::numberBetween(1, 15),
+            ]);
         } catch (NoDefinedFactoryException $e) {
             $this->assertSame("No model definition was defined for the model: 'DogModelStub'.", $e->getMessage());
             $this->assertSame('DogModelStub', $e->getModel());
diff --git a/tests/factories/definition.php b/tests/factories/definition.php
index ee610e6..1d2dd43 100644
--- a/tests/factories/definition.php
+++ b/tests/factories/definition.php
@@ -25,7 +25,9 @@
     'active'  => Faker::boolean(),
     'email'   => Faker::email(),
     'profile' => 'factory|ProfileModelStub',
-]);
+])->setCallback(function ($obj) {
+    $obj->test = 'foo';
+});
 
 $fm->define('group:UserModelStub')->addDefinition('address', Faker::address());
 
@@ -38,10 +40,7 @@
     $obj->test = 'bar';
 });
 
-$fm->define('foo:DogModelStub')->setDefinitions([
-    'name' => Faker::firstNameMale(),
-    'age'  => Faker::numberBetween(1, 15),
-]);
+$fm->define('noattributes:UserModelStub')->clearDefinitions();
 
 $fm->define('ExampleCallbackStub')->setCallback(function ($obj, $saved) {
     $obj->callback = 'yaycalled';