diff --git a/caravel/models.py b/caravel/models.py
index 4c7ee4419b6af..6a73cb2223e2c 100644
--- a/caravel/models.py
+++ b/caravel/models.py
@@ -315,7 +315,7 @@ def json_data(self):
             'dashboard_title': self.dashboard_title,
             'slug': self.slug,
             'slices': [slc.data for slc in self.slices],
-            'position_json': json.loads(self.position_json),
+            'position_json': json.loads(self.position_json) if self.position_json else [],
         }
         return json.dumps(d)
 
diff --git a/caravel/views.py b/caravel/views.py
index 0d27812a583d0..7d236c064af48 100644
--- a/caravel/views.py
+++ b/caravel/views.py
@@ -508,7 +508,7 @@ def pre_add(self, obj):
             obj.slug = re.sub(r'\W+', '', obj.slug)
 
     def pre_update(self, obj):
-        check_ownership()
+        check_ownership(obj)
         self.pre_add(obj)