diff --git a/docs/guide/defining-documents.rst b/docs/guide/defining-documents.rst
index 3c276869..7b8dcd5b 100644
--- a/docs/guide/defining-documents.rst
+++ b/docs/guide/defining-documents.rst
@@ -46,6 +46,12 @@ are as follows:
 * :class:`~mongoengine.EmbeddedDocumentField`
 * :class:`~mongoengine.ReferenceField`
 * :class:`~mongoengine.GenericReferenceField`
+* :class:`~mongoengine.BooleanField`
+* :class:`~mongoengine.GeoLocationField`
+* :class:`~mongoengine.FileField`
+* :class:`~mongoengine.EmailField`
+* :class:`~mongoengine.SortedListField`
+* :class:`~mongoengine.BinaryField`
 
 Field arguments
 ---------------
diff --git a/mongoengine/base.py b/mongoengine/base.py
index c8c162b4..b6d5a63b 100644
--- a/mongoengine/base.py
+++ b/mongoengine/base.py
@@ -24,8 +24,8 @@ class BaseField(object):
     _index_with_types = True
     
     def __init__(self, db_field=None, name=None, required=False, default=None, 
-                 unique=False, unique_with=None, primary_key=False, validation=None,
-                 choices=None):
+                 unique=False, unique_with=None, primary_key=False,
+                 validation=None, choices=None):
         self.db_field = (db_field or name) if not primary_key else '_id'
         if name:
             import warnings
@@ -86,13 +86,15 @@ class BaseField(object):
         # check choices
         if self.choices is not None:
             if value not in self.choices:
-                raise ValidationError("Value must be one of %s."%unicode(self.choices))
+                raise ValidationError("Value must be one of %s."
+                    % unicode(self.choices))
         
         # check validation argument
         if self.validation is not None:
             if callable(self.validation):
                 if not self.validation(value):
-                    raise ValidationError('Value does not match custom validation method.')
+                    raise ValidationError('Value does not match custom' \
+                                          'validation method.')
             else:
                 raise ValueError('validation argument must be a callable.')
     
diff --git a/mongoengine/fields.py b/mongoengine/fields.py
index 5893049d..ebefbb75 100644
--- a/mongoengine/fields.py
+++ b/mongoengine/fields.py
@@ -530,17 +530,21 @@ class GridFSProxy(object):
 
     def __init__(self):
         self.fs = gridfs.GridFS(_get_db())  # Filesystem instance
-        self.newfile = None                # Used for partial writes
+        self.newfile = None                 # Used for partial writes
         self.grid_id = None                 # Store GridFS id for file
 
     def __getattr__(self, name):
-        obj = self.fs.get(self.grid_id)
+        obj = self.get()
         if name in dir(obj):
             return getattr(obj, name)
 
     def __get__(self, instance, value):
         return self
 
+    def get(self, id=None):
+        try: return self.fs.get(id or self.grid_id)
+        except: return None # File has been deleted
+
     def new_file(self, **kwargs):
         self.newfile = self.fs.new_file(**kwargs)
         self.grid_id = self.newfile._id
@@ -561,11 +565,17 @@ class GridFSProxy(object):
         self.newfile.writelines(lines) 
 
     def read(self):
-        return self.fs.get(self.grid_id).read()
+        try: return self.get().read()
+        except: return None
 
     def delete(self):
-        # Delete file from GridFS
+        # Delete file from GridFS, FileField still remains
         self.fs.delete(self.grid_id)
+        self.grid_id = None
+
+    def replace(self, file, **kwargs):
+        self.delete()
+        self.put(file, **kwargs)
 
     def close(self):
         if self.newfile:
@@ -601,7 +611,7 @@ class FileField(BaseField):
 
     def to_python(self, value):
         # Use stored value (id) to lookup file in GridFS
-        return self.gridfs.fs.get(value)
+        return self.gridfs.get()
 
     def validate(self, value):
         assert isinstance(value, GridFSProxy)
diff --git a/tests/fields.py b/tests/fields.py
index e22e6ddd..8dddcb3e 100644
--- a/tests/fields.py
+++ b/tests/fields.py
@@ -649,7 +649,10 @@ class FieldTest(unittest.TestCase):
         self.assertTrue(streamfile == result)
         self.assertEquals(result.file.read(), text + more_text)
         self.assertEquals(result.file.content_type, content_type)
-        result.file.delete() # Remove file from GridFS
+        result.file.delete()
+
+        # Ensure deleted file returns None
+        self.assertTrue(result.file.read() == None)
 
         setfile = SetFile()
         setfile.file = text
@@ -658,7 +661,15 @@ class FieldTest(unittest.TestCase):
         result = SetFile.objects.first()
         self.assertTrue(setfile == result)
         self.assertEquals(result.file.read(), text)
-        result.file.delete() # Remove file from GridFS
+
+        # Try replacing file with new one
+        result.file.replace(more_text)
+        result.save()
+        result.validate()
+        result = SetFile.objects.first()
+        self.assertTrue(setfile == result)
+        self.assertEquals(result.file.read(), more_text)
+        result.file.delete() 
 
         PutFile.drop_collection()
         StreamFile.drop_collection()