diff --git a/cryptography/hazmat/primitives/hashes.py b/cryptography/hazmat/primitives/hashes.py
index 97e9bf4..a50017b 100644
--- a/cryptography/hazmat/primitives/hashes.py
+++ b/cryptography/hazmat/primitives/hashes.py
@@ -21,6 +21,8 @@
 @interfaces.register(interfaces.HashContext)
 class Hash(object):
     def __init__(self, algorithm, backend=None, ctx=None):
+        if not isinstance(algorithm, interfaces.HashAlgorithm):
+            raise TypeError("Expected instance of interfaces.HashAlgorithm.")
         self.algorithm = algorithm
 
         if backend is None:
diff --git a/tests/hazmat/primitives/test_hash_vectors.py b/tests/hazmat/primitives/test_hash_vectors.py
index 5c3e72d..fca839c 100644
--- a/tests/hazmat/primitives/test_hash_vectors.py
+++ b/tests/hazmat/primitives/test_hash_vectors.py
@@ -29,7 +29,7 @@
             "SHA1LongMsg.rsp",
             "SHA1ShortMsg.rsp",
         ],
-        hashes.SHA1,
+        hashes.SHA1(),
         only_if=lambda backend: backend.hashes.supported(hashes.SHA1),
         skip_message="Does not support SHA1",
     )
@@ -43,7 +43,7 @@
             "SHA224LongMsg.rsp",
             "SHA224ShortMsg.rsp",
         ],
-        hashes.SHA224,
+        hashes.SHA224(),
         only_if=lambda backend: backend.hashes.supported(hashes.SHA224),
         skip_message="Does not support SHA224",
     )
@@ -57,7 +57,7 @@
             "SHA256LongMsg.rsp",
             "SHA256ShortMsg.rsp",
         ],
-        hashes.SHA256,
+        hashes.SHA256(),
         only_if=lambda backend: backend.hashes.supported(hashes.SHA256),
         skip_message="Does not support SHA256",
     )
@@ -71,7 +71,7 @@
             "SHA384LongMsg.rsp",
             "SHA384ShortMsg.rsp",
         ],
-        hashes.SHA384,
+        hashes.SHA384(),
         only_if=lambda backend: backend.hashes.supported(hashes.SHA384),
         skip_message="Does not support SHA384",
     )
@@ -85,7 +85,7 @@
             "SHA512LongMsg.rsp",
             "SHA512ShortMsg.rsp",
         ],
-        hashes.SHA512,
+        hashes.SHA512(),
         only_if=lambda backend: backend.hashes.supported(hashes.SHA512),
         skip_message="Does not support SHA512",
     )
@@ -98,13 +98,13 @@
         [
             "ripevectors.txt",
         ],
-        hashes.RIPEMD160,
+        hashes.RIPEMD160(),
         only_if=lambda backend: backend.hashes.supported(hashes.RIPEMD160),
         skip_message="Does not support RIPEMD160",
     )
 
     test_RIPEMD160_long_string = generate_long_string_hash_test(
-        hashes.RIPEMD160,
+        hashes.RIPEMD160(),
         "52783243c1697bdbe16d37f97f68f08325dc1528",
         only_if=lambda backend: backend.hashes.supported(hashes.RIPEMD160),
         skip_message="Does not support RIPEMD160",
@@ -118,13 +118,13 @@
         [
             "iso-test-vectors.txt",
         ],
-        hashes.Whirlpool,
+        hashes.Whirlpool(),
         only_if=lambda backend: backend.hashes.supported(hashes.Whirlpool),
         skip_message="Does not support Whirlpool",
     )
 
     test_whirlpool_long_string = generate_long_string_hash_test(
-        hashes.Whirlpool,
+        hashes.Whirlpool(),
         ("0c99005beb57eff50a7cf005560ddf5d29057fd86b2"
          "0bfd62deca0f1ccea4af51fc15490eddc47af32bb2b"
          "66c34ff9ad8c6008ad677f77126953b226e4ed8b01"),
@@ -140,7 +140,7 @@
         [
             "rfc-1321.txt",
         ],
-        hashes.MD5,
+        hashes.MD5(),
         only_if=lambda backend: backend.hashes.supported(hashes.MD5),
         skip_message="Does not support MD5",
     )
diff --git a/tests/hazmat/primitives/test_hashes.py b/tests/hazmat/primitives/test_hashes.py
index 43a0f44..07ab248 100644
--- a/tests/hazmat/primitives/test_hashes.py
+++ b/tests/hazmat/primitives/test_hashes.py
@@ -25,35 +25,36 @@
 from .utils import generate_base_hash_test
 
 
-class TestBaseHash(object):
-    def test_base_hash_reject_unicode(self, backend):
-        m = hashes.Hash(hashes.SHA1, backend=backend)
+class TestHashContext(object):
+    def test_hash_reject_unicode(self, backend):
+        m = hashes.Hash(hashes.SHA1(), backend=backend)
         with pytest.raises(TypeError):
             m.update(six.u("\u00FC"))
 
-
-class TestCopyHash(object):
     def test_copy_backend_object(self):
         pretend_hashes = pretend.stub(copy_ctx=lambda a: "copiedctx")
         pretend_backend = pretend.stub(hashes=pretend_hashes)
         pretend_ctx = pretend.stub()
-        h = hashes.Hash(hashes.SHA1, backend=pretend_backend, ctx=pretend_ctx)
+        h = hashes.Hash(hashes.SHA1(), backend=pretend_backend,
+                        ctx=pretend_ctx)
         assert h._backend is pretend_backend
         assert h.copy()._backend is h._backend
 
-
-class TestDefaultBackendSHA1(object):
     def test_default_backend_creation(self):
         """
         This test assumes the presence of SHA1 in the default backend.
         """
-        h = hashes.Hash(hashes.SHA1)
+        h = hashes.Hash(hashes.SHA1())
         assert h._backend is _default_backend
 
+    def test_hash_algorithm_instance(self):
+        with pytest.raises(TypeError):
+            hashes.Hash(hashes.SHA1)
+
 
 class TestSHA1(object):
     test_SHA1 = generate_base_hash_test(
-        hashes.SHA1,
+        hashes.SHA1(),
         digest_size=20,
         block_size=64,
         only_if=lambda backend: backend.hashes.supported(hashes.SHA1),
@@ -63,7 +64,7 @@
 
 class TestSHA224(object):
     test_SHA224 = generate_base_hash_test(
-        hashes.SHA224,
+        hashes.SHA224(),
         digest_size=28,
         block_size=64,
         only_if=lambda backend: backend.hashes.supported(hashes.SHA224),
@@ -73,7 +74,7 @@
 
 class TestSHA256(object):
     test_SHA256 = generate_base_hash_test(
-        hashes.SHA256,
+        hashes.SHA256(),
         digest_size=32,
         block_size=64,
         only_if=lambda backend: backend.hashes.supported(hashes.SHA256),
@@ -83,7 +84,7 @@
 
 class TestSHA384(object):
     test_SHA384 = generate_base_hash_test(
-        hashes.SHA384,
+        hashes.SHA384(),
         digest_size=48,
         block_size=128,
         only_if=lambda backend: backend.hashes.supported(hashes.SHA384),
@@ -93,7 +94,7 @@
 
 class TestSHA512(object):
     test_SHA512 = generate_base_hash_test(
-        hashes.SHA512,
+        hashes.SHA512(),
         digest_size=64,
         block_size=128,
         only_if=lambda backend: backend.hashes.supported(hashes.SHA512),
@@ -103,7 +104,7 @@
 
 class TestRIPEMD160(object):
     test_RIPEMD160 = generate_base_hash_test(
-        hashes.RIPEMD160,
+        hashes.RIPEMD160(),
         digest_size=20,
         block_size=64,
         only_if=lambda backend: backend.hashes.supported(hashes.RIPEMD160),
@@ -113,7 +114,7 @@
 
 class TestWhirlpool(object):
     test_Whirlpool = generate_base_hash_test(
-        hashes.Whirlpool,
+        hashes.Whirlpool(),
         digest_size=64,
         block_size=64,
         only_if=lambda backend: backend.hashes.supported(hashes.Whirlpool),
@@ -123,7 +124,7 @@
 
 class TestMD5(object):
     test_MD5 = generate_base_hash_test(
-        hashes.MD5,
+        hashes.MD5(),
         digest_size=16,
         block_size=64,
         only_if=lambda backend: backend.hashes.supported(hashes.MD5),
diff --git a/tests/hazmat/primitives/utils.py b/tests/hazmat/primitives/utils.py
index f562956..efc5fbf 100644
--- a/tests/hazmat/primitives/utils.py
+++ b/tests/hazmat/primitives/utils.py
@@ -66,12 +66,12 @@
     return test_hash
 
 
-def hash_test(backend, hash_cls, params, only_if, skip_message):
+def hash_test(backend, algorithm, params, only_if, skip_message):
     if only_if is not None and not only_if(backend):
         pytest.skip(skip_message)
     msg = params[0]
     md = params[1]
-    m = hashes.Hash(hash_cls, backend=backend)
+    m = hashes.Hash(algorithm, backend=backend)
     m.update(binascii.unhexlify(msg))
     expected_md = md.replace(" ", "").lower().encode("ascii")
     assert m.finalize() == binascii.unhexlify(expected_md)