news.texi                   |  5 +++++
 pygost/__init__.py          |  2 +-
 pygost/gost3410.py          |  1 +
 pygost/gost34112012.py      |  5 +++--
 pygost/test_gost34112012.py | 16 ++++++++++++++++

diff --git a/news.texi b/news.texi
index dbe4f8680df1e02347ffa129060f50259492b94578f4514db4aa4953e5b8e082..110503cd5e1bbc517f983e6fda843ea389281fe8d4da757bbbe825a552ac1a73 100644
--- a/news.texi
+++ b/news.texi
@@ -3,6 +3,11 @@ @unnumbered News
 
 @table @strong
 
+@anchor{Release 5.12}
+@item 5.12
+Fixed incorrect digest calculation when using @code{GOST34112012*.update()}
+method.
+
 @anchor{Release 5.11}
 @item 5.11
 @code{gost34112012}'s @code{update()}/@code{digest()} methods are
diff --git a/pygost/__init__.py b/pygost/__init__.py
index 627cad094e6b33f9c44960db0244e5bb5318724a708d570d98090e7593d9a43e..032adc8b2e2c305420fd59ba7828193e9f85561ac7ebde32c5e3e982cf7f749d 100644
--- a/pygost/__init__.py
+++ b/pygost/__init__.py
@@ -3,4 +3,4 @@
 PyGOST is free software: see the file COPYING for copying conditions.
 """
 
-__version__ = "5.11"
+__version__ = "5.12"
diff --git a/pygost/gost3410.py b/pygost/gost3410.py
index bb41eb4916240d569d873cbe37a82f5eef40daabbeeaefbc7339f138dd64d224..c3c63a0f48e0c231bed9c768a85df14e5bcb9112f2ae3f53f45d1a9a50f93a2f 100644
--- a/pygost/gost3410.py
+++ b/pygost/gost3410.py
@@ -55,6 +55,7 @@     :param long e, d: coefficients of the equation of the elliptic curve in
                       the twisted Edwards form
     :param str name: human-readable curve name
     """
+
     def __init__(self, p, q, a, b, x, y, cofactor=1, e=None, d=None, name=None):
         self.p = p
         self.q = q
diff --git a/pygost/gost34112012.py b/pygost/gost34112012.py
index decd962e1b6608520c95d008d6a18e587e4877a97ae3bbbfb049e0b913027f27..caa6556e2cf86d4befec228b3c3d9127146d26a899490cdf3d2efc52eac87a72 100644
--- a/pygost/gost34112012.py
+++ b/pygost/gost34112012.py
@@ -268,8 +268,9 @@     def update(self, data):
         """Update state with the new data
         """
         if len(self.buf) > 0:
-            self.buf += data[:BLOCKSIZE - len(self.buf)]
-            data = data[BLOCKSIZE - len(self.buf):]
+            chunk_len = BLOCKSIZE - len(self.buf)
+            self.buf += data[:chunk_len]
+            data = data[chunk_len:]
             if len(self.buf) == BLOCKSIZE:
                 self._update_block(self.buf)
                 self.buf = b""
diff --git a/pygost/test_gost34112012.py b/pygost/test_gost34112012.py
index 05a7113561f9b1021ca2f6616ac92bb0fb32f86a68f8b9e47d8dd4de37b76072..11843dad8224749eaba7633c315b62c954608ed1d9a1412edad1136df41cae47 100644
--- a/pygost/test_gost34112012.py
+++ b/pygost/test_gost34112012.py
@@ -14,6 +14,8 @@ #
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+from os import urandom
+from random import randint
 from unittest import skip
 from unittest import TestCase
 import hmac
@@ -35,6 +37,20 @@         m.update(b"foobar")
         c.update(b"foo")
         c.update(b"bar")
         self.assertSequenceEqual(m.digest(), c.digest())
+
+
+class TestSymmetric(TestCase):
+    def runTest(self):
+        chunks = []
+        for _ in range(randint(1, 10)):
+            chunks.append(urandom(randint(20, 80)))
+        m = GOST34112012256()
+        for chunk in chunks:
+            m.update(chunk)
+        self.assertSequenceEqual(
+            m.hexdigest(),
+            GOST34112012256(b"".join(chunks)).hexdigest(),
+        )
 
 
 class TestHMAC(TestCase):