diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index 5e29cd5b5f..189f0ba4ad 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -695,7 +695,7 @@ class DecimalField(Field):
                 _("This value must be a decimal number."))
 
     def _format(self, value):
-        if isinstance(value, basestring):
+        if isinstance(value, basestring) or value is None:
             return value
         else:
             return self.format_number(value)
@@ -716,8 +716,7 @@ class DecimalField(Field):
         return u"%.*f" % (self.decimal_places, value)
 
     def get_db_prep_save(self, value):
-        if value is not None:
-            value = self._format(value)
+        value = self._format(value)
         return super(DecimalField, self).get_db_prep_save(value)
 
     def get_db_prep_lookup(self, lookup_type, value):
diff --git a/tests/regressiontests/model_fields/tests.py b/tests/regressiontests/model_fields/tests.py
index e279a0669f..c2ba9ee008 100644
--- a/tests/regressiontests/model_fields/tests.py
+++ b/tests/regressiontests/model_fields/tests.py
@@ -15,4 +15,21 @@ Decimal("3.14")
 Traceback (most recent call last):
 ...
 ValidationError: [u'This value must be a decimal number.']
+
+>>> f = DecimalField(max_digits=5, decimal_places=1)
+>>> x = f.to_python(2)
+>>> y = f.to_python('2.6')
+
+>>> f.get_db_prep_save(x)
+u'2.0'
+>>> f.get_db_prep_save(y)
+u'2.6'
+>>> f.get_db_prep_save(None)
+>>> f.get_db_prep_lookup('exact', x)
+[u'2.0']
+>>> f.get_db_prep_lookup('exact', y)
+[u'2.6']
+>>> f.get_db_prep_lookup('exact', None)
+[None]
+
 """