diff --git a/cryptography/hazmat/primitives/hashes.py b/cryptography/hazmat/primitives/hashes.py
index bdad5e1..c774811 100644
--- a/cryptography/hazmat/primitives/hashes.py
+++ b/cryptography/hazmat/primitives/hashes.py
@@ -34,7 +34,7 @@
         if ctx is None:
             self._ctx = self._backend.hashes.create_ctx(self.algorithm)
         else:
-            self._ctx = None
+            self._ctx = ctx
 
     def update(self, data):
         if isinstance(data, six.text_type):
diff --git a/tests/hazmat/primitives/utils.py b/tests/hazmat/primitives/utils.py
index 0f97595..9327b0e 100644
--- a/tests/hazmat/primitives/utils.py
+++ b/tests/hazmat/primitives/utils.py
@@ -155,6 +155,12 @@
     assert m != m_copy
     assert m._ctx != m_copy._ctx
 
+    m.update(b"abc")
+    copy = m.copy()
+    copy.update(b"123")
+    m.update(b"123")
+    assert copy.finalize() == m.finalize()
+
 
 def generate_long_string_hash_test(hash_factory, md, only_if=None,
                                    skip_message=None):