diff --git a/boards/forms.py b/boards/forms.py
--- a/boards/forms.py
+++ b/boards/forms.py
@@ -39,7 +39,7 @@ class PostForm(forms.Form):
 
 
 class ThreadForm(PostForm):
-    regex_tags = re.compile(r'^[\w\s]+$')
+    regex_tags = re.compile(ur'^[\w\s\d]+$', re.UNICODE)
 
     tags = forms.CharField(max_length=100)
 
diff --git a/boards/models.py b/boards/models.py
--- a/boards/models.py
+++ b/boards/models.py
@@ -1,27 +1,31 @@
 import os
 from random import random
 import re
-from django.db import models
-from django.utils import timezone
 import time
 import math
-import markdown
-from markdown.inlinepatterns import Pattern
-from markdown.util import etree
+
+from django.db import models
+from django.http import Http404
+from django.utils import timezone
+from markupfield.fields import MarkupField
 
 from neboard import settings
-from markupfield.fields import MarkupField
+import thumbs
 
-import thumbs
 
 NO_PARENT = -1
 NO_IP = '0.0.0.0'
 UNKNOWN_UA = ''
+ALL_PAGES = -1
+OPENING_POST_WEIGHT = 5
+IMAGES_DIRECTORY = 'images/'
+FILE_EXTENSION_DELIMITER = '.'
+
+REGEX_PRETTY = re.compile(r'^\d(0)+$')
+REGEX_SAME = re.compile(r'^(.)\1+$')
 
 
 class PostManager(models.Manager):
-    ALL_PAGES = -1
-
     def create_post(self, title, text, image=None, parent_id=NO_PARENT,
                     ip=NO_IP, tags=None):
         post = self.create(title=title,
@@ -62,7 +66,7 @@ class PostManager(models.Manager):
             threads = self.filter(parent=NO_PARENT)
         threads = threads.order_by('-last_edit_time')
 
-        if page != self.ALL_PAGES:
+        if page != ALL_PAGES:
             thread_count = len(threads)
 
             if page < self.get_thread_page_count(tag=tag):
@@ -76,6 +80,9 @@ class PostManager(models.Manager):
     def get_thread(self, opening_post_id):
         opening_post = self.get(id=opening_post_id)
 
+        if not opening_post:
+            raise Http404
+
         if opening_post.parent == NO_PARENT:
             replies = self.filter(parent=opening_post_id)
 
@@ -151,8 +158,6 @@ class Tag(models.Model):
     section. There can be multiple tags for each message
     """
 
-    OPENING_POST_WEIGHT = 5
-
     objects = TagManager()
 
     name = models.CharField(max_length=100)
@@ -182,19 +187,16 @@ class Tag(models.Model):
 class Post(models.Model):
     """A post is a message."""
 
-    IMAGES_DIRECTORY = 'images/'
-    FILE_EXTENSION_DELIMITER = '.'
-
     objects = PostManager()
 
     def _update_image_filename(self, filename):
         """Get unique image filename"""
 
-        path = self.IMAGES_DIRECTORY
+        path = IMAGES_DIRECTORY
         new_name = str(int(time.mktime(time.gmtime())))
         new_name += str(int(random() * 1000))
-        new_name += self.FILE_EXTENSION_DELIMITER
-        new_name += filename.split(self.FILE_EXTENSION_DELIMITER)[-1:][0]
+        new_name += FILE_EXTENSION_DELIMITER
+        new_name += filename.split(FILE_EXTENSION_DELIMITER)[-1:][0]
 
         return os.path.join(path, new_name)
 
@@ -209,9 +211,6 @@ class Post(models.Model):
     tags = models.ManyToManyField(Tag)
     last_edit_time = models.DateTimeField()
 
-    regex_pretty = re.compile(r'^\d(0)+$')
-    regex_same = re.compile(r'^(.)\1+$')
-
     def __unicode__(self):
         return self.title + ' (' + self.text.raw + ')'
 
@@ -243,8 +242,8 @@ class Post(models.Model):
         first = self.id == 1
 
         id_str = str(self.id)
-        pretty = self.regex_pretty.match(id_str)
-        same_digits = self.regex_same.match(id_str)
+        pretty = REGEX_PRETTY.match(id_str)
+        same_digits = REGEX_SAME.match(id_str)
 
         return first or pretty or same_digits
 
diff --git a/boards/tests.py b/boards/tests.py
--- a/boards/tests.py
+++ b/boards/tests.py
@@ -1,3 +1,4 @@
+# coding=utf-8
 from django.utils.unittest import TestCase
 from django.test.client import Client
 
@@ -6,6 +7,11 @@ import boards
 from boards.models import Post, Admin, Tag
 from neboard import settings
 
+TEST_TEXT = 'test text'
+
+NEW_THREAD_PAGE = '/'
+HTTP_CODE_REDIRECT = 302
+
 
 class BoardTests(TestCase):
     def _create_post(self):
@@ -119,8 +125,6 @@ class BoardTests(TestCase):
     def test_pages(self):
         """Test that the thread list is properly split into pages"""
 
-        PAGE_NUMBER = 2
-
         for i in range(settings.MAX_THREAD_COUNT):
             self._create_post()
 
@@ -130,4 +134,29 @@ class BoardTests(TestCase):
         first_post = posts_in_second_page[0]
 
         self.assertEqual(all_threads[settings.THREADS_PER_PAGE].id,
-                                     first_post.id)
\ No newline at end of file
+                         first_post.id)
+
+    def test_post_validation(self):
+        """Test the validation of the post form"""
+
+        Post.objects.all().delete()
+
+        client = Client()
+
+        valid_tags = u'tag1 tag_2 тег_3'
+        invalid_tags = u'$%_356 ---'
+
+        response = client.post(NEW_THREAD_PAGE, {'title': 'test title',
+                                                 'text': TEST_TEXT,
+                                                 'tags': valid_tags})
+        self.assertEqual(response.status_code, HTTP_CODE_REDIRECT,
+                         msg='Posting new message failed: got code ' +
+                             str(response.status_code))
+
+        self.assertEqual(1, Post.objects.count(),
+                         msg='No posts were created')
+
+        response = client.post(NEW_THREAD_PAGE, {'text': TEST_TEXT,
+                                                 'tags': invalid_tags})
+        self.assertEqual(1, Post.objects.count(), msg='The validation passed '
+                                                      'where it should fail')
\ No newline at end of file
diff --git a/boards/views.py b/boards/views.py
--- a/boards/views.py
+++ b/boards/views.py
@@ -110,7 +110,6 @@ def thread(request, post_id):
     if request.method == 'POST':
         return new_post(request, post_id)
     else:
-        # TODO Show 404 if there is no such thread
         posts = Post.objects.get_thread(post_id)
 
         context = RequestContext(request)