diff --git a/attic/crypto.py b/attic/crypto.py
index 8d7b32040..862ca616b 100644
--- a/attic/crypto.py
+++ b/attic/crypto.py
@@ -22,6 +22,12 @@ bytes_to_long = lambda x, offset=0: _long.unpack_from(x, offset)[0]
 long_to_bytes = lambda x: _long.pack(x)
 
 
+def num_aes_blocks(length):
+    """Return the number of AES blocks required to encrypt/decrypt *length* bytes of data
+    """
+    return (length + 15) // 16
+
+
 def pbkdf2_sha256(password, salt, iterations, size):
     key = create_string_buffer(size)
     rv = libcrypto.PKCS5_PBKDF2_HMAC(password, len(password), salt, len(salt), iterations, libcrypto.EVP_sha256(), size, key)
diff --git a/attic/testsuite/archiver.py b/attic/testsuite/archiver.py
index 3dd898cab..048aaba39 100644
--- a/attic/testsuite/archiver.py
+++ b/attic/testsuite/archiver.py
@@ -7,10 +7,12 @@ import shutil
 import tempfile
 import time
 import unittest
+from hashlib import sha256
 from attic import xattr
 from attic.archiver import Archiver
 from attic.repository import Repository
 from attic.testsuite import AtticTestCase
+from attic.crypto import bytes_to_long, num_aes_blocks
 
 try:
     import llfuse
@@ -89,7 +91,6 @@ class ArchiverTestCase(AtticTestCase):
             sys.stdout, sys.stderr = stdout, stderr
 
     def create_src_archive(self, name):
-        self.attic('init', self.repository_location)
         self.attic('create', self.repository_location + '::' + name, src_dir)
 
     def create_regual_file(self, name, size=0):
@@ -201,6 +202,7 @@ class ArchiverTestCase(AtticTestCase):
         self.assert_equal(repository._len(), 1)
 
     def test_corrupted_repository(self):
+        self.attic('init', self.repository_location)
         self.create_src_archive('test')
         self.attic('verify', self.repository_location + '::test')
         name = sorted(os.listdir(os.path.join(self.tmpdir, 'repository', 'data', '0')), reverse=True)[0]
@@ -211,6 +213,7 @@ class ArchiverTestCase(AtticTestCase):
         self.attic('verify', self.repository_location + '::test', exit_code=1)
 
     def test_readonly_repository(self):
+        self.attic('init', self.repository_location)
         self.create_src_archive('test')
         os.system('chmod -R ugo-w ' + self.repository_path)
         try:
@@ -252,6 +255,41 @@ class ArchiverTestCase(AtticTestCase):
             # Give the daemon some time to exit
             time.sleep(.2)
 
+    def verify_aes_counter_uniqueness(self, method):
+        seen = set()  # Chunks already seen
+        used = set()  # counter values already used
+
+        def verify_uniqueness():
+            repository = Repository(self.repository_path)
+            for key, _ in repository.index.iteritems():
+                data = repository.get(key)
+                hash = sha256(data).digest()
+                if not hash in seen:
+                    seen.add(hash)
+                    num_blocks = num_aes_blocks(len(data) - 41)
+                    start = bytes_to_long(data[33:41])
+                    for counter in range(start, start + num_blocks):
+                        self.assert_not_in(counter, used)
+                        used.add(counter)
+
+        self.create_test_files()
+        os.environ['ATTIC_PASSPHRASE'] = 'passphrase'
+        self.attic('init', '--encryption=' + method, self.repository_location)
+        verify_uniqueness()
+        self.attic('create', self.repository_location + '::test', 'input')
+        verify_uniqueness()
+        self.attic('create', self.repository_location + '::test.2', 'input')
+        verify_uniqueness()
+        self.attic('delete', self.repository_location + '::test.2')
+        verify_uniqueness()
+
+    def test_aes_counter_uniqueness_keyfile(self):
+        self.verify_aes_counter_uniqueness('keyfile')
+
+    def test_aes_counter_uniqueness_passphrase(self):
+        self.verify_aes_counter_uniqueness('passphrase')
+
+
 
 class RemoteArchiverTestCase(ArchiverTestCase):
     prefix = '__testsuite__:'