diff --git a/isso/db/__init__.py b/isso/db/__init__.py
index 56e8f4f..f1030f2 100644
--- a/isso/db/__init__.py
+++ b/isso/db/__init__.py
@@ -1,6 +1,9 @@
 # -*- encoding: utf-8 -*-
 
 import sqlite3
+import logging
+
+logger = logging.getLogger("isso")
 
 class IssoDBException(Exception):
     pass
@@ -11,12 +14,24 @@ from isso.db.threads import Threads
 
 class SQLite3:
 
+    MAX_VERSION = 1
+
     def __init__(self, path, conf):
 
         self.path = path
         self.conf = conf
         self.mode = 1
 
+        rv = self.execute([
+            "SELECT name FROM sqlite_master"
+            "   WHERE type='table' AND name IN ('threads', 'comments')"]
+        ).fetchall()
+
+        if rv:
+            self.migrate(to=SQLite3.MAX_VERSION)
+        else:
+            self.execute("PRAGMA user_version = %i" % SQLite3.MAX_VERSION)
+
         self.threads = Threads(self)
         self.comments = Comments(self)
 
@@ -34,3 +49,24 @@ class SQLite3:
 
         with sqlite3.connect(self.path) as con:
             return con.execute(sql, args)
+
+    @property
+    def version(self):
+        return self.execute("PRAGMA user_version").fetchone()[0]
+
+    def migrate(self, to):
+
+        if self.version >= to:
+            return
+
+        logger.info("migrate database from version %i to %i", self.version, to)
+
+        if self.version == 0:
+
+            from isso.utils import Bloomfilter
+            bf = buffer(Bloomfilter(iterable=["127.0.0.0"]).array)
+
+            with sqlite3.connect(self.path) as con:
+                con.execute('UPDATE comments SET voters=?', (bf, ))
+                con.execute('PRAGMA user_version = 1')
+                logger.info("%i rows changed", con.total_changes)
diff --git a/isso/utils/__init__.py b/isso/utils/__init__.py
index de3be2b..1751be4 100644
--- a/isso/utils/__init__.py
+++ b/isso/utils/__init__.py
@@ -56,15 +56,31 @@ class Bloomfilter:
     of space efficiency (array is saved for each comment) and 11 hash functions
     because of best overall false-positive rate in that range.
 
+    >>> bf = Bloomfilter()
+    >>> bf.add("127.0.0.1")
+    >>> not any(map(bf.__contains__, ("1.2.%i.4" for i in range(256))))
+    True
+
+    >>> bf = Bloomfilter()
+    >>> for i in range(256):
+    ...     bf.add("1.2.%i.4" % i)
+    ...
+    >>> len(bf)
+    256
+    >>> "1.2.3.4" in bf
+    True
+    >>> "127.0.0.1" in bf
+    False
+
     -- via Raymond Hettinger
        http://code.activestate.com/recipes/577684-bloom-filter/
     """
 
-    def __init__(self, array=bytearray(256), elements=0, iterable=()):
-        self.array = array
+    def __init__(self, array=None, elements=0, iterable=()):
+        self.array = array or bytearray(256)
         self.elements = elements
         self.k = 11
-        self.m = len(array) * 8
+        self.m = len(self.array) * 8
 
         for item in iterable:
             self.add(item)