diff --git a/CHANGES.rst b/CHANGES.rst
index 52a1924..a4e0122 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -4,6 +4,18 @@ Changelog
 Here you can see the full list of changes between each SQLAlchemy-Utils release.
 
 
+0.31.2 (2015-10-30)
+^^^^^^^^^^^^^^^^^^^
+
+- Fixed observes crashing when observable root_obj is ``None`` (#168)
+
+
+0.31.1 (2015-10-26)
+^^^^^^^^^^^^^^^^^^^
+
+- Column observers only notified when actual changes have been made to underlying columns (#138)
+
+
 0.31.0 (2015-09-17)
 ^^^^^^^^^^^^^^^^^^^
 
diff --git a/sqlalchemy_utils/__init__.py b/sqlalchemy_utils/__init__.py
index 9e2c582..cab47cc 100644
--- a/sqlalchemy_utils/__init__.py
+++ b/sqlalchemy_utils/__init__.py
@@ -93,4 +93,4 @@ from .types import (  # noqa
     WeekDaysType
 )
 
-__version__ = '0.31.1'
+__version__ = '0.31.2'
diff --git a/sqlalchemy_utils/observer.py b/sqlalchemy_utils/observer.py
index bd7c1de..0e0db69 100644
--- a/sqlalchemy_utils/observer.py
+++ b/sqlalchemy_utils/observer.py
@@ -245,9 +245,10 @@ class PropertyObserver(object):
                     root_objs = [root_objs]
 
                 for root_obj in root_objs:
-                    args = self.get_callback_args(root_obj, callback)
-                    if args:
-                        yield args
+                    if root_obj:
+                        args = self.get_callback_args(root_obj, callback)
+                        if args:
+                            yield args
 
     def get_callback_args(self, root_obj, callback):
         session = sa.orm.object_session(root_obj)
diff --git a/tests/observes/test_o2o_o2o.py b/tests/observes/test_o2o_o2o.py
new file mode 100644
index 0000000..a923295
--- /dev/null
+++ b/tests/observes/test_o2o_o2o.py
@@ -0,0 +1,53 @@
+import sqlalchemy as sa
+
+from sqlalchemy_utils.observer import observes
+from tests import TestCase
+
+
+class TestObservesForOneToManyToOneToMany(TestCase):
+    dns = 'postgres://postgres@localhost/sqlalchemy_utils_test'
+
+    def create_models(self):
+        class Device(self.Base):
+            __tablename__ = 'device'
+            id = sa.Column(sa.Integer, primary_key=True)
+            name = sa.Column(sa.String)
+
+        class Order(self.Base):
+            __tablename__ = 'order'
+            id = sa.Column(sa.Integer, primary_key=True)
+
+            device_id = sa.Column(
+                'device', sa.ForeignKey('device.id'), nullable=False
+            )
+            device = sa.orm.relationship('Device', backref='orders')
+
+        class SalesInvoice(self.Base):
+            __tablename__ = 'sales_invoice'
+            id = sa.Column(sa.Integer, primary_key=True)
+            order_id = sa.Column(
+                'order',
+                sa.ForeignKey('order.id'),
+                nullable=False
+            )
+            order = sa.orm.relationship(
+                'Order',
+                backref=sa.orm.backref(
+                    'invoice',
+                    uselist=False
+                )
+            )
+            device_name = sa.Column(sa.String)
+
+            @observes('order.device')
+            def process_device(self, device):
+                self.device_name = device.name
+
+        self.Device = Device
+        self.Order = Order
+        self.SalesInvoice = SalesInvoice
+
+    def test_observable_root_obj_is_none(self):
+        order = self.Order(device=self.Device(name='Something'))
+        self.session.add(order)
+        self.session.flush()