diff --git a/sqlalchemy_utils/functions/__init__.py b/sqlalchemy_utils/functions/__init__.py
index 74e41d1..bc6caeb 100644
--- a/sqlalchemy_utils/functions/__init__.py
+++ b/sqlalchemy_utils/functions/__init__.py
@@ -23,27 +23,25 @@ from .orm import (
 )
 
 __all__ = (
-    create_database,
-    create_mock_engine,
-    database_exists,
-    declarative_base,
-    defer_except,
-    drop_database,
-    escape_like,
-    getdotattr,
-    has_changes,
-    identity,
-    is_auto_assigned_date_column,
-    is_indexed_foreign_key,
-    mock_engine,
-    naturally_equivalent,
-    non_indexed_foreign_keys,
-    primary_keys,
-    QuerySorterException,
-    render_expression,
-    render_statement,
-    sort_query,
-    table_name,
+    'create_database',
+    'create_mock_engine',
+    'database_exists',
+    'declarative_base',
+    'defer_except',
+    'drop_database',
+    'escape_like',
+    'getdotattr',
+    'has_changes',
+    'identity',
+    'is_auto_assigned_date_column',
+    'is_indexed_foreign_key',
+    'mock_engine',
+    'naturally_equivalent',
+    'non_indexed_foreign_keys',
+    'primary_keys',
+    'QuerySorterException',
+    'render_expression',
+    'render_statement',
+    'sort_query',
+    'table_name',
 )
-
-
diff --git a/sqlalchemy_utils/functions/orm.py b/sqlalchemy_utils/functions/orm.py
index 8811dd3..1a276d7 100644
--- a/sqlalchemy_utils/functions/orm.py
+++ b/sqlalchemy_utils/functions/orm.py
@@ -1,4 +1,9 @@
+try:
+    from collections import OrderedDict
+except ImportError:
+    from ordereddict import OrderedDict
 from functools import partial
+from inspect import isclass
 from operator import attrgetter
 import sqlalchemy as sa
 from sqlalchemy import inspect
@@ -9,13 +14,19 @@ from sqlalchemy.orm.query import _ColumnEntity
 from sqlalchemy.orm.util import AliasedInsp
 
 
-def primary_keys(class_):
+def primary_keys(obj_or_class):
     """
-    Returns all primary keys for given declarative class.
+    Return an OrderedDict of all primary keys for given declarative class or
+    object.
     """
-    for column in class_.__table__.c:
+    if not isclass(obj_or_class):
+        obj_or_class = obj_or_class.__class__
+
+    columns = OrderedDict()
+    for key, column in sa.inspect(obj_or_class).columns.items():
         if column.primary_key:
-            yield column
+            columns[key] = column
+    return columns
 
 
 def table_name(obj):
@@ -325,8 +336,8 @@ def identity(obj_or_class):
     :param obj: SQLAlchemy declarative model object
     """
     return tuple(
-        getattr(obj_or_class, column.name)
-        for column in primary_keys(obj_or_class)
+        getattr(obj_or_class, column_key)
+        for column_key in primary_keys(obj_or_class).keys()
     )
 
 
diff --git a/tests/functions/test_identity.py b/tests/functions/test_identity.py
index 74094fb..f220f0d 100644
--- a/tests/functions/test_identity.py
+++ b/tests/functions/test_identity.py
@@ -3,15 +3,7 @@ from sqlalchemy_utils.functions import identity
 from tests import TestCase
 
 
-class TestIdentity(TestCase):
-    def create_models(self):
-        class Building(self.Base):
-            __tablename__ = 'building'
-            id = sa.Column(sa.Integer, primary_key=True)
-            name = sa.Column(sa.Unicode(255))
-
-        self.Building = Building
-
+class IdentityTestCase(TestCase):
     def test_for_transient_class_without_id(self):
         assert identity(self.Building()) == (None, )
 
@@ -24,3 +16,23 @@ class TestIdentity(TestCase):
 
     def test_identity_for_class(self):
         assert identity(self.Building) == (self.Building.id, )
+
+
+class TestIdentity(IdentityTestCase):
+    def create_models(self):
+        class Building(self.Base):
+            __tablename__ = 'building'
+            id = sa.Column(sa.Integer, primary_key=True)
+            name = sa.Column(sa.Unicode(255))
+
+        self.Building = Building
+
+
+class TestIdentityWithColumnAlias(IdentityTestCase):
+    def create_models(self):
+        class Building(self.Base):
+            __tablename__ = 'building'
+            id = sa.Column('_id', sa.Integer, primary_key=True)
+            name = sa.Column(sa.Unicode(255))
+
+        self.Building = Building