diff --git a/cryptography/fernet.py b/cryptography/fernet.py
index 064acee..880d96f 100644
--- a/cryptography/fernet.py
+++ b/cryptography/fernet.py
@@ -10,6 +10,10 @@
 from cryptography.hazmat.primitives.block import BlockCipher, ciphers, modes
 
 
+class InvalidToken(Exception):
+    pass
+
+
 class Fernet(object):
     def __init__(self, key):
         super(Fernet, self).__init__()
@@ -23,6 +27,9 @@
         return self._encrypt_from_parts(data, current_time, iv)
 
     def _encrypt_from_parts(self, data, current_time, iv):
+        if isinstance(data, six.text_type):
+            raise TypeError("Unicode-objects must be encoded before encryption")
+
         padder = padding.PKCS7(ciphers.AES.block_size).padder()
         padded_data = padder.update(data) + padder.finalize()
         encryptor = BlockCipher(
@@ -41,28 +48,43 @@
         )
 
     def decrypt(self, data, ttl=None, current_time=None):
-        # TODO: whole function is a giant hack job with no error checking
+        if isinstance(data, six.text_type):
+            raise TypeError("Unicode-objects must be encoded before decryption")
+
         if current_time is None:
             current_time = int(time.time())
-        data = base64.urlsafe_b64decode(data)
+
+        try:
+            data = base64.urlsafe_b64decode(data)
+        except TypeError:
+            raise InvalidToken
+
         assert six.indexbytes(data, 0) == 0x80
         timestamp = data[1:9]
         iv = data[9:25]
         ciphertext = data[25:-32]
         if ttl is not None:
             if struct.unpack(">Q", timestamp)[0] + ttl < current_time:
-                raise ValueError
+                raise InvalidToken
         h = HMAC(self.signing_key, digestmod=hashes.SHA256)
         h.update(data[:-32])
         hmac = h.digest()
+
         if not constant_time_compare(hmac, data[-32:]):
-            raise ValueError
+            raise InvalidToken
+
         decryptor = BlockCipher(
             ciphers.AES(self.encryption_key), modes.CBC(iv)
         ).decryptor()
         plaintext_padded = decryptor.update(ciphertext) + decryptor.finalize()
         unpadder = padding.PKCS7(ciphers.AES.block_size).unpadder()
-        return unpadder.update(plaintext_padded) + unpadder.finalize()
+
+        unpadded = unpadder.update(plaintext_padded)
+        try:
+            unpadded += unpadder.finalize()
+        except ValueError:
+            raise InvalidToken
+        return unpadded
 
 
 def constant_time_compare(a, b):
diff --git a/tests/test_fernet.py b/tests/test_fernet.py
index 382a232..1507171 100644
--- a/tests/test_fernet.py
+++ b/tests/test_fernet.py
@@ -9,10 +9,11 @@
 
 import six
 
-from cryptography.fernet import Fernet
+from cryptography.fernet import Fernet, InvalidToken
 
 
-def json_parametrize(keys, path):
+def json_parametrize(keys, fname):
+    path = os.path.join(os.path.dirname(__file__), "vectors", "fernet", fname)
     with open(path) as f:
         data = json.load(f)
     return pytest.mark.parametrize(keys, [
@@ -23,8 +24,7 @@
 
 class TestFernet(object):
     @json_parametrize(
-        ("secret", "now", "iv", "src", "token"),
-        os.path.join(os.path.dirname(__file__), "vectors", "fernet", "generate.json")
+        ("secret", "now", "iv", "src", "token"), "generate.json",
     )
     def test_generate(self, secret, now, iv, src, token):
         f = Fernet(base64.urlsafe_b64decode(secret.encode("ascii")))
@@ -36,8 +36,7 @@
         assert actual_token == token
 
     @json_parametrize(
-        ("secret", "now", "src", "ttl_sec", "token"),
-        os.path.join(os.path.dirname(__file__), "vectors", "fernet", "verify.json")
+        ("secret", "now", "src", "ttl_sec", "token"), "verify.json",
     )
     def test_verify(self, secret, now, src, ttl_sec, token):
         f = Fernet(base64.urlsafe_b64decode(secret.encode("ascii")))
@@ -47,3 +46,20 @@
             current_time=calendar.timegm(iso8601.parse_date(now).utctimetuple())
         )
         assert payload == src
+
+    @json_parametrize(("secret", "token", "now", "ttl_sec"), "invalid.json")
+    def test_invalid(self, secret, token, now, ttl_sec):
+        f = Fernet(base64.urlsafe_b64decode(secret.encode("ascii")))
+        with pytest.raises(InvalidToken):
+            f.decrypt(
+                token.encode("ascii"),
+                ttl=ttl_sec,
+                current_time=calendar.timegm(iso8601.parse_date(now).utctimetuple())
+            )
+
+    def test_unicode(self):
+        f = Fernet(b"\x00" * 32)
+        with pytest.raises(TypeError):
+            f.encrypt(six.u(""))
+        with pytest.raises(TypeError):
+            f.decrypt(six.u(""))
diff --git a/tests/vectors/fernet/invalid.json b/tests/vectors/fernet/invalid.json
new file mode 100644
index 0000000..d80e7b4
--- /dev/null
+++ b/tests/vectors/fernet/invalid.json
@@ -0,0 +1,58 @@
+[
+  {
+    "desc": "incorrect mac",
+    "token": "gAAAAAAdwJ6xAAECAwQFBgcICQoLDA0OD3HkMATM5lFqGaerZ-fWPAl1-szkFVzXTuGb4hR8AKtwcaX1YdykQUFBQUFBQUFBQQ==",
+    "now": "1985-10-26T01:20:01-07:00",
+    "ttl_sec": 60,
+    "secret": "cw_0x689RpI-jtRR7oE8h_eQsKImvJapLeSbXpwF4e4="
+  },
+  {
+    "desc": "too short",
+    "token": "gAAAAAAdwJ6xAAECAwQFBgcICQoLDA0OD3HkMATM5lFqGaerZ-fWPA==",
+    "now": "1985-10-26T01:20:01-07:00",
+    "ttl_sec": 60,
+    "secret": "cw_0x689RpI-jtRR7oE8h_eQsKImvJapLeSbXpwF4e4="
+  },
+  {
+    "desc": "invalid base64",
+    "token": "%%%%%%%%%%%%%AECAwQFBgcICQoLDA0OD3HkMATM5lFqGaerZ-fWPAl1-szkFVzXTuGb4hR8AKtwcaX1YdykRtfsH-p1YsUD2Q==",
+    "now": "1985-10-26T01:20:01-07:00",
+    "ttl_sec": 60,
+    "secret": "cw_0x689RpI-jtRR7oE8h_eQsKImvJapLeSbXpwF4e4="
+  },
+  {
+    "desc": "payload size not multiple of block size",
+    "token": "gAAAAAAdwJ6xAAECAwQFBgcICQoLDA0OD3HkMATM5lFqGaerZ-fWPOm73QeoCk9uGib28Xe5vz6oxq5nmxbx_v7mrfyudzUm",
+    "now": "1985-10-26T01:20:01-07:00",
+    "ttl_sec": 60,
+    "secret": "cw_0x689RpI-jtRR7oE8h_eQsKImvJapLeSbXpwF4e4="
+  },
+  {
+    "desc": "payload padding error",
+    "token": "gAAAAAAdwJ6xAAECAwQFBgcICQoLDA0ODz4LEpdELGQAad7aNEHbf-JkLPIpuiYRLQ3RtXatOYREu2FWke6CnJNYIbkuKNqOhw==",
+    "now": "1985-10-26T01:20:01-07:00",
+    "ttl_sec": 60,
+    "secret": "cw_0x689RpI-jtRR7oE8h_eQsKImvJapLeSbXpwF4e4="
+  },
+  {
+    "desc": "far-future TS (unacceptable clock skew)",
+    "token": "gAAAAAAdwStRAAECAwQFBgcICQoLDA0OD3HkMATM5lFqGaerZ-fWPAnja1xKYyhd-Y6mSkTOyTGJmw2Xc2a6kBd-iX9b_qXQcw==",
+    "now": "1985-10-26T01:20:01-07:00",
+    "ttl_sec": 60,
+    "secret": "cw_0x689RpI-jtRR7oE8h_eQsKImvJapLeSbXpwF4e4="
+  },
+  {
+    "desc": "expired TTL",
+    "token": "gAAAAAAdwJ6xAAECAwQFBgcICQoLDA0OD3HkMATM5lFqGaerZ-fWPAl1-szkFVzXTuGb4hR8AKtwcaX1YdykRtfsH-p1YsUD2Q==",
+    "now": "1985-10-26T01:21:31-07:00",
+    "ttl_sec": 60,
+    "secret": "cw_0x689RpI-jtRR7oE8h_eQsKImvJapLeSbXpwF4e4="
+  },
+  {
+    "desc": "incorrect IV (causes padding error)",
+    "token": "gAAAAAAdwJ6xBQECAwQFBgcICQoLDA0OD3HkMATM5lFqGaerZ-fWPAkLhFLHpGtDBRLRTZeUfWgHSv49TF2AUEZ1TIvcZjK1zQ==",
+    "now": "1985-10-26T01:20:01-07:00",
+    "ttl_sec": 60,
+    "secret": "cw_0x689RpI-jtRR7oE8h_eQsKImvJapLeSbXpwF4e4="
+  }
+]