2 files changed, 7 insertions, 4 deletions
diff --git a/cryptography/hazmat/primitives/ciphers/base.py b/cryptography/hazmat/primitives/ciphers/base.py
index 794d0191..0fe11996 100644
--- a/cryptography/hazmat/primitives/ciphers/base.py
+++ b/cryptography/hazmat/primitives/ciphers/base.py
@@ -13,6 +13,7 @@
 
 from __future__ import absolute_import, division, print_function
 
+from cryptography.exceptions import AlreadyFinalized
 from cryptography.hazmat.primitives import interfaces
 
 
@@ -45,12 +46,12 @@ class _CipherContext(object):
 
     def update(self, data):
         if self._ctx is None:
-            raise ValueError("Context was already finalized")
+            raise AlreadyFinalized("Context was already finalized")
         return self._ctx.update(data)
 
     def finalize(self):
         if self._ctx is None:
-            raise ValueError("Context was already finalized")
+            raise AlreadyFinalized("Context was already finalized")
         data = self._ctx.finalize()
         self._ctx = None
         return data
diff --git a/cryptography/hazmat/primitives/hashes.py b/cryptography/hazmat/primitives/hashes.py
index b8de6c4b..86c9fe2e 100644
--- a/cryptography/hazmat/primitives/hashes.py
+++ b/cryptography/hazmat/primitives/hashes.py
@@ -39,19 +39,21 @@ class Hash(object):
 
     def update(self, data):
         if self._ctx is None:
-            raise AlreadyFinalized()
+            raise AlreadyFinalized("Context was already finalized")
         if isinstance(data, six.text_type):
             raise TypeError("Unicode-objects must be encoded before hashing")
         self._ctx.update(data)
 
     def copy(self):
         if self._ctx is None:
-            raise AlreadyFinalized()
+            raise AlreadyFinalized("Context was already finalized")
         return Hash(
             self.algorithm, backend=self._backend, ctx=self._ctx.copy()
         )
 
     def finalize(self):
+        if self._ctx is None:
+            raise AlreadyFinalized("Context was already finalized")
         digest = self._ctx.finalize()
         self._ctx = None
         return digest