diff --git a/osmtm/models.py b/osmtm/models.py
index 5cc7dc0a..56e25836 100644
--- a/osmtm/models.py
+++ b/osmtm/models.py
@@ -372,7 +372,7 @@ def __init__(self, x, y, zoom, geometry=None, properties=None):
         self.y = y
         self.zoom = zoom
         if properties is not None:
-            self.extra_properties = unicode(_dumps(properties))
+            self.extra_properties = unicode(_dumps(properties['extra_properties']))
         if geometry is None:
             geometry = self.to_polygon()
             multipolygon = MultiPolygon([geometry])