diff --git a/oslo_serialization/base64.py b/oslo_serialization/base64.py
index 7ff6e57..401e036 100644
--- a/oslo_serialization/base64.py
+++ b/oslo_serialization/base64.py
@@ -22,6 +22,7 @@ Utilities to encode and decode Base64.
 from __future__ import absolute_import
 
 import base64
+import binascii
 
 import six
 
@@ -64,13 +65,16 @@ def decode_as_bytes(encoded):
     :returns: decoded bytes string (bytes)
 
     Use decode_as_text() to get the decoded string as text.
+
+    A TypeError is raised if the input is invalid (or incorrectly padded).
     """
     if isinstance(encoded, bytes):
         encoded = encoded.decode('ascii')
-    if six.PY2:
-        return base64.decodestring(encoded)
-    else:
+    try:
         return base64.b64decode(encoded)
+    except binascii.Error as e:
+        # Transform this exception for consistency.
+        raise TypeError(str(e))
 
 
 def decode_as_text(encoded, encoding='utf-8'):
diff --git a/oslo_serialization/tests/test_base64.py b/oslo_serialization/tests/test_base64.py
index 8b29d70..645f2ee 100644
--- a/oslo_serialization/tests/test_base64.py
+++ b/oslo_serialization/tests/test_base64.py
@@ -13,8 +13,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import binascii
-
 from oslo_serialization import base64
 from oslotest import base as test_base
 
@@ -48,7 +46,7 @@ class Base64Tests(test_base.BaseTestCase):
                          base64.decode_as_bytes(u'dGV4dA=='))
 
     def test_decode_as_bytes__error(self):
-        self.assertRaises(binascii.Error,
+        self.assertRaises(TypeError,
                           base64.decode_as_bytes,
                           'hello world')