diff --git a/facho/model/fields/function.py b/facho/model/fields/function.py
index 34e3195..9ea2ac3 100644
--- a/facho/model/fields/function.py
+++ b/facho/model/fields/function.py
@@ -2,7 +2,7 @@ from .field import Field
 from .model import Model
 
 class Function(Field):
-    def __init__(self, getter, setter=None, field=None):
+    def __init__(self, getter=None, setter=None, field=None):
         self.field = field
         self.getter = getter
         self.setter = setter
@@ -12,6 +12,12 @@ class Function(Field):
             return self
         assert self.name is not None
 
+        if self.getter is None and self.field is None:
+            return None
+
+        if self.getter is None and self.field is not None:
+            return Model(self.field)
+
         if self.field is None:
             return self._call(inst, self.getter, self.name)
         else:
diff --git a/tests/test_model.py b/tests/test_model.py
index fa92e9f..cfcd65c 100644
--- a/tests/test_model.py
+++ b/tests/test_model.py
@@ -257,4 +257,18 @@ def test_field_function_setter():
     person = Person()
     person.password = 'calculate'
     assert '<Person hash="calculate+2"/>' == person.to_xml()
+
+def test_field_function_only_setter():
+    class Person(facho.model.Model):
+        __name__ = 'Person'
+
+        hash = fields.Attribute('hash')
+        password = fields.Function(setter='set_hash')
+
+        def set_hash(self, name, value):
+            self.hash = "%s+2" % (value)
+
+    person = Person()
+    person.password = 'calculate'
+    assert '<Person hash="calculate+2"/>' == person.to_xml()