diff --git a/src/modelsubquery/functions.py b/src/modelsubquery/functions.py
index 1c8dbde..9051d13 100644
--- a/src/modelsubquery/functions.py
+++ b/src/modelsubquery/functions.py
@@ -13,7 +13,7 @@ def _model_fields(model, fields):
     then return all the declared fields.
     """
     # TODO: the pk/id field should always be returned
-    declared = {f.column for f in model._meta.get_fields()}
+    declared = {f.column for f in model._meta.get_fields() if f.concrete}
     if fields is None:
         return declared
 
diff --git a/testproject/testapp/models.py b/testproject/testapp/models.py
index 0760033..6e29f72 100644
--- a/testproject/testapp/models.py
+++ b/testproject/testapp/models.py
@@ -31,3 +31,8 @@ class Person(models.Model):
     birth = models.DateField(default=date.today)
 
     objects = PersonQuerySet.as_manager()
+
+
+class Shelve(models.Model):
+    title = models.CharField(max_length=100)
+    books = models.ManyToManyField("Book", related_name="shelves")