diff --git a/beets/dbcore/db.py b/beets/dbcore/db.py
index cbdaf5a7f..a5f29e0ed 100644
--- a/beets/dbcore/db.py
+++ b/beets/dbcore/db.py
@@ -152,8 +152,15 @@ class Model(object):
     def __setitem__(self, key, value):
         """Assign the value for a field.
         """
-        source = self._values_fixed if key in self._fields \
-                 else self._values_flex
+        # Choose where to place the value. If the corresponding field
+        # has a type, filter the value.
+        if key in self._fields:
+            source = self._values_fixed
+            value = self._fields[key].normalize(value)
+        else:
+            source = self._values_flex
+
+        # Assign value and possibly mark as dirty.
         old_value = source.get(key)
         source[key] = value
         if old_value != value:
diff --git a/beets/dbcore/types.py b/beets/dbcore/types.py
index 165c0b601..ccd260c0d 100644
--- a/beets/dbcore/types.py
+++ b/beets/dbcore/types.py
@@ -24,8 +24,8 @@ from beets.util import str2bool
 
 class Type(object):
     """An object encapsulating the type of a model field. Includes
-    information about how to store the value in the database, query,
-    format, and parse a given field.
+    information about how to store, query, format, and parse a given
+    field.
     """
 
     sql = None
@@ -36,6 +36,10 @@ class Type(object):
     """The `Query` subclass to be used when querying the field.
     """
 
+    null = None
+    """The value to be exposed when the underlying value is None.
+    """
+
     def format(self, value):
         """Given a value of this type, produce a Unicode string
         representing the value. This is used in template evaluation.
@@ -48,6 +52,16 @@ class Type(object):
         """
         raise NotImplementedError()
 
+    def normalize(self, value):
+        """Given a value that will be assigned into a field of this
+        type, normalize the value to have the appropriate type. This
+        base implementation only reinterprets `None`.
+        """
+        if value is None:
+            return self.null
+        else:
+            return value
+
 
 
 # Reusable types.
@@ -58,6 +72,7 @@ class Integer(Type):
     """
     sql = u'INTEGER'
     query = query.NumericQuery
+    null = 0
 
     def format(self, value):
         return unicode(value or 0)
@@ -93,9 +108,14 @@ class ScaledInt(Integer):
 
 
 class Id(Integer):
-    """An integer used as the row key for a SQLite table.
+    """An integer used as the row id or a foreign key in a SQLite table.
+    This type is nullable: None values are not translated to zero.
     """
-    sql = u'INTEGER PRIMARY KEY'
+    null = None
+
+    def __init__(self, primary=True):
+        if primary:
+            self.sql = u'INTEGER PRIMARY KEY'
 
 
 class Float(Type):
@@ -103,6 +123,7 @@ class Float(Type):
     """
     sql = u'REAL'
     query = query.NumericQuery
+    null = 0.0
 
     def format(self, value):
         return u'{0:.1f}'.format(value or 0.0)
@@ -119,6 +140,7 @@ class String(Type):
     """
     sql = u'TEXT'
     query = query.SubstringQuery
+    null = u''
 
     def format(self, value):
         return unicode(value) if value else u''
@@ -132,6 +154,7 @@ class Boolean(Type):
     """
     sql = u'INTEGER'
     query = query.BooleanQuery
+    null = False
 
     def format(self, value):
         return unicode(bool(value))
diff --git a/beets/library.py b/beets/library.py
index fe4d9e0b5..349f8459a 100644
--- a/beets/library.py
+++ b/beets/library.py
@@ -79,6 +79,7 @@ class SingletonQuery(dbcore.Query):
 class DateType(types.Type):
     sql = u'REAL'
     query = dbcore.query.DateQuery
+    null = 0.0
 
     def format(self, value):
         return time.strftime(beets.config['time_format'].get(unicode),
@@ -95,7 +96,7 @@ class DateType(types.Type):
             try:
                 return float(string)
             except ValueError:
-                return 0.0
+                return self.null
 
 
 class PathType(types.Type):
@@ -122,9 +123,9 @@ class PathType(types.Type):
 # - Is the field writable?
 # - Does the field reflect an attribute of a MediaFile?
 ITEM_FIELDS = [
-    ('id',       types.Id(),      False, False),
+    ('id',       types.Id(True),  False, False),
     ('path',     PathType(),      False, False),
-    ('album_id', types.Integer(), False, False),
+    ('album_id', types.Id(False), False, False),
 
     ('title',                types.String(),     True, True),
     ('artist',               types.String(),     True, True),
@@ -192,9 +193,9 @@ ITEM_KEYS          = [f[0] for f in ITEM_FIELDS]
 # The third entry in each tuple indicates whether the field reflects an
 # identically-named field in the items table.
 ALBUM_FIELDS = [
-    ('id',      types.Id(), False),
-    ('artpath', PathType(), False),
-    ('added',   DateType(), True),
+    ('id',      types.Id(True), False),
+    ('artpath', PathType(),     False),
+    ('added',   DateType(),     True),
 
     ('albumartist',        types.String(),     True),
     ('albumartist_sort',   types.String(),     True),
diff --git a/test/test_dbcore.py b/test/test_dbcore.py
index 85fb94f87..2f4af7472 100644
--- a/test/test_dbcore.py
+++ b/test/test_dbcore.py
@@ -219,6 +219,16 @@ class ModelTest(_common.TestCase):
         with self.assertRaises(KeyError):
             del model['field_one']
 
+    def test_null_value_normalization_by_type(self):
+        model = TestModel1()
+        model.field_one = None
+        self.assertEqual(model.field_one, 0)
+
+    def test_null_value_stays_none_for_untyped_field(self):
+        model = TestModel1()
+        model.foo = None
+        self.assertEqual(model.foo, None)
+
 
 class FormatTest(_common.TestCase):
     def test_format_fixed_field(self):