diff --git a/src/Illuminate/Database/Eloquent/Relations/MorphTo.php b/src/Illuminate/Database/Eloquent/Relations/MorphTo.php
index 2739786d5e7e..d0465d590927 100644
--- a/src/Illuminate/Database/Eloquent/Relations/MorphTo.php
+++ b/src/Illuminate/Database/Eloquent/Relations/MorphTo.php
@@ -194,9 +194,9 @@ protected function matchToMorphParents($type, Collection $results)
      */
     public function associate($model)
     {
-        $this->parent->setAttribute($this->foreignKey, $model->getKey());
+        $this->parent->setAttribute($this->foreignKey, $model instanceof Model ? $model->getKey() : null);
 
-        $this->parent->setAttribute($this->morphType, $model->getMorphClass());
+        $this->parent->setAttribute($this->morphType, $model instanceof Model ? $model->getMorphClass() : null);
 
         return $this->parent->setRelation($this->relation, $model);
     }
diff --git a/tests/Database/DatabaseEloquentMorphToTest.php b/tests/Database/DatabaseEloquentMorphToTest.php
index ac9df28d7d97..9cfdb2283a30 100644
--- a/tests/Database/DatabaseEloquentMorphToTest.php
+++ b/tests/Database/DatabaseEloquentMorphToTest.php
@@ -57,6 +57,20 @@ public function testAssociateMethodSetsForeignKeyAndTypeOnModel()
         $relation->associate($associate);
     }
 
+    public function testAssociateMethodIgnoresNullValue()
+    {
+        $parent = m::mock('Illuminate\Database\Eloquent\Model');
+        $parent->shouldReceive('getAttribute')->once()->with('foreign_key')->andReturn('foreign.value');
+
+        $relation = $this->getRelationAssociate($parent);
+
+        $parent->shouldReceive('setAttribute')->once()->with('foreign_key', null);
+        $parent->shouldReceive('setAttribute')->once()->with('morph_type', null);
+        $parent->shouldReceive('setRelation')->once()->with('relation', null);
+
+        $relation->associate(null);
+    }
+
     public function testDissociateMethodDeletesUnsetsKeyAndTypeOnModel()
     {
         $parent = m::mock('Illuminate\Database\Eloquent\Model');