diff --git a/src/dynamodb_encryption_sdk/delegated_keys/__init__.py b/src/dynamodb_encryption_sdk/delegated_keys/__init__.py
index 9c2ad28e..ac57a207 100644
--- a/src/dynamodb_encryption_sdk/delegated_keys/__init__.py
+++ b/src/dynamodb_encryption_sdk/delegated_keys/__init__.py
@@ -13,7 +13,7 @@
 """Delegated keys."""
 import abc
 try:  # Python 3.5.0 and 3.5.1 have incompatible typing modules
-    from typing import Dict, Text  # noqa pylint: disable=unused-import
+    from typing import Dict, Optional, Text  # noqa pylint: disable=unused-import
 except ImportError:  # pragma: no cover
     # We only actually need these imports when running the mypy checks
     pass
@@ -43,17 +43,24 @@ class DelegatedKey(object):
     a ``NotImplementedError`` detailing this.
     """
 
-    #: Most delegated keys should not be used with RawCryptographicMaterials.
-    allowed_for_raw_materials = False
-
     @abc.abstractproperty
     def algorithm(self):
         # type: () -> Text
         """Text description of algorithm used by this delegated key."""
 
+    @property
+    def allowed_for_raw_materials(self):
+        # type: () -> bool
+        """Most delegated keys should not be used with RawCryptographicMaterials.
+
+        :returns: False
+        :rtype: bool
+        """
+        return False
+
     @classmethod
-    def generate(cls, algorithm, key_length):
-        # type: (Text, int) -> None
+    def generate(cls, algorithm, key_length):  # type: ignore
+        # type: (Text, int) -> DelegatedKey
         # pylint: disable=unused-argument,no-self-use
         """Generate an instance of this DelegatedKey using the specified algorithm and key length.
 
@@ -64,8 +71,8 @@ def generate(cls, algorithm, key_length):
         """
         _raise_not_implemented('generate')
 
-    def encrypt(self, algorithm, name, plaintext, additional_associated_data=None):
-        # type: (Text, Text, bytes, Dict[Text, Text]) -> bytes
+    def encrypt(self, algorithm, name, plaintext, additional_associated_data=None):  # type: ignore
+        # type: (Text, Text, bytes, Optional[Dict[Text, Text]]) -> bytes
         # pylint: disable=unused-argument,no-self-use
         """Encrypt data.
 
@@ -79,8 +86,8 @@ def encrypt(self, algorithm, name, plaintext, additional_associated_data=None):
         """
         _raise_not_implemented('encrypt')
 
-    def decrypt(self, algorithm, name, ciphertext, additional_associated_data=None):
-        # type: (Text, Text, bytes, Dict[Text, Text]) -> bytes
+    def decrypt(self, algorithm, name, ciphertext, additional_associated_data=None):  # type: ignore
+        # type: (Text, Text, bytes, Optional[Dict[Text, Text]]) -> bytes
         # pylint: disable=unused-argument,no-self-use
         """Encrypt data.
 
@@ -94,8 +101,8 @@ def decrypt(self, algorithm, name, ciphertext, additional_associated_data=None):
         """
         _raise_not_implemented('decrypt')
 
-    def wrap(self, algorithm, content_key, additional_associated_data=None):
-        # type: (Text, bytes, Dict[Text, Text]) -> bytes
+    def wrap(self, algorithm, content_key, additional_associated_data=None):  # type: ignore
+        # type: (Text, bytes, Optional[Dict[Text, Text]]) -> bytes
         # pylint: disable=unused-argument,no-self-use
         """Wrap content key.
 
@@ -108,8 +115,15 @@ def wrap(self, algorithm, content_key, additional_associated_data=None):
         """
         _raise_not_implemented('wrap')
 
-    def unwrap(self, algorithm, wrapped_key, wrapped_key_algorithm, wrapped_key_type, additional_associated_data=None):
-        # type: (Text, bytes, Text, EncryptionKeyType, Dict[Text, Text]) -> DelegatedKey
+    def unwrap(  # type: ignore
+            self,
+            algorithm,
+            wrapped_key,
+            wrapped_key_algorithm,
+            wrapped_key_type,
+            additional_associated_data=None
+    ):
+        # type: (Text, bytes, Text, EncryptionKeyType, Optional[Dict[Text, Text]]) -> DelegatedKey
         # pylint: disable=unused-argument,no-self-use
         """Wrap content key.
 
@@ -125,7 +139,7 @@ def unwrap(self, algorithm, wrapped_key, wrapped_key_algorithm, wrapped_key_type
         """
         _raise_not_implemented('unwrap')
 
-    def sign(self, algorithm, data):
+    def sign(self, algorithm, data):  # type: ignore
         # type: (Text, bytes) -> bytes
         # pylint: disable=unused-argument,no-self-use
         """Sign data.
@@ -137,7 +151,7 @@ def sign(self, algorithm, data):
         """
         _raise_not_implemented('sign')
 
-    def verify(self, algorithm, signature, data):
+    def verify(self, algorithm, signature, data):  # type: ignore
         # type: (Text, bytes, bytes) -> None
         # pylint: disable=unused-argument,no-self-use
         """Sign data.
@@ -148,10 +162,10 @@ def verify(self, algorithm, signature, data):
         """
         _raise_not_implemented('verify')
 
-    def signing_algorithm(self):
+    def signing_algorithm(self):  # type: ignore
         # type: () -> Text
         # pylint: disable=no-self-use
-        """Provides a description that can inform an appropriate cryptographic materials
+        """Provide a description that can inform an appropriate cryptographic materials
         provider about how to build a DelegatedKey for signature verification. If implemented,
         the return value of this method is included in the material description written to
         the encrypted item.
diff --git a/src/dynamodb_encryption_sdk/delegated_keys/jce.py b/src/dynamodb_encryption_sdk/delegated_keys/jce.py
index 13802852..4ee676a9 100644
--- a/src/dynamodb_encryption_sdk/delegated_keys/jce.py
+++ b/src/dynamodb_encryption_sdk/delegated_keys/jce.py
@@ -228,6 +228,7 @@ def generate(cls, algorithm, key_length=None):
 
     @property
     def allowed_for_raw_materials(self):
+        # type: () -> bool
         """Only ``JceNameLocalDelegatedKey`` backed by AES keys are allowed to be used with
         ``RawCryptographicMaterials``.
 
@@ -237,7 +238,7 @@ def allowed_for_raw_materials(self):
         return self.algorithm == 'AES'
 
     def _encrypt(self, algorithm, name, plaintext, additional_associated_data=None):
-        # type: (Text, Text, bytes, Dict[Text, Text]) -> bytes
+        # type: (Text, Text, bytes, Optional[Dict[Text, Text]]) -> bytes
         # pylint: disable=unused-argument
         """
         Encrypt data.
@@ -255,7 +256,7 @@ def _encrypt(self, algorithm, name, plaintext, additional_associated_data=None):
         return encryptor.encrypt(self.__key, plaintext)
 
     def _decrypt(self, algorithm, name, ciphertext, additional_associated_data=None):
-        # type: (Text, Text, bytes, Dict[Text, Text]) -> bytes
+        # type: (Text, Text, bytes, Optional[Dict[Text, Text]]) -> bytes
         # pylint: disable=unused-argument
         """Encrypt data.
 
@@ -271,7 +272,7 @@ def _decrypt(self, algorithm, name, ciphertext, additional_associated_data=None)
         return decryptor.decrypt(self.__key, ciphertext)
 
     def _wrap(self, algorithm, content_key, additional_associated_data=None):
-        # type: (Text, bytes, Dict[Text, Text]) -> bytes
+        # type: (Text, bytes, Optional[Dict[Text, Text]]) -> bytes
         # pylint: disable=unused-argument
         """Wrap content key.
 
@@ -288,7 +289,7 @@ def _wrap(self, algorithm, content_key, additional_associated_data=None):
         )
 
     def _unwrap(self, algorithm, wrapped_key, wrapped_key_algorithm, wrapped_key_type, additional_associated_data=None):
-        # type: (Text, bytes, Text, EncryptionKeyType, Dict[Text, Text]) -> DelegatedKey
+        # type: (Text, bytes, Text, EncryptionKeyType, Optional[Dict[Text, Text]]) -> DelegatedKey
         # pylint: disable=unused-argument
         """Wrap content key.
 
@@ -341,7 +342,7 @@ def _verify(self, algorithm, signature, data):
 
     def _signing_algorithm(self):
         # type: () -> Text
-        """Provides a description that can inform an appropriate cryptographic materials
+        """Provide a description that can inform an appropriate cryptographic materials
         provider about how to build a ``JceNameLocalDelegatedKey`` for signature verification.
         The return value of this method is included in the material description written to
         the encrypted item.
diff --git a/src/dynamodb_encryption_sdk/encrypted/client.py b/src/dynamodb_encryption_sdk/encrypted/client.py
index b7d6b170..06b0066b 100644
--- a/src/dynamodb_encryption_sdk/encrypted/client.py
+++ b/src/dynamodb_encryption_sdk/encrypted/client.py
@@ -17,7 +17,7 @@
 import botocore
 
 try:  # Python 3.5.0 and 3.5.1 have incompatible typing modules
-    from typing import Any, Callable, Dict, Optional  # noqa pylint: disable=unused-import
+    from typing import Any, Callable, Dict, Iterator, Optional  # noqa pylint: disable=unused-import
 except ImportError:  # pragma: no cover
     # We only actually need these imports when running the mypy checks
     pass
@@ -88,7 +88,7 @@ def __getattr__(self, name):
         return getattr(self._paginator, name)
 
     def paginate(self, **kwargs):
-        # type: (**Any) -> Dict
+        # type: (**Any) -> Iterator[Dict]
         # TODO: narrow this down
         """Create an iterator that will paginate through responses from the underlying paginator,
         transparently decrypting any returned items.
diff --git a/src/dynamodb_encryption_sdk/encrypted/resource.py b/src/dynamodb_encryption_sdk/encrypted/resource.py
index 1e78a3b5..18dad1e5 100644
--- a/src/dynamodb_encryption_sdk/encrypted/resource.py
+++ b/src/dynamodb_encryption_sdk/encrypted/resource.py
@@ -17,6 +17,12 @@
 from boto3.resources.base import ServiceResource
 from boto3.resources.collection import CollectionManager
 
+try:  # Python 3.5.0 and 3.5.1 have incompatible typing modules
+    from typing import Optional  # noqa pylint: disable=unused-import
+except ImportError:  # pragma: no cover
+    # We only actually need these imports when running the mypy checks
+    pass
+
 from dynamodb_encryption_sdk.internal.utils import (
     crypto_config_from_cache, decrypt_batch_get_item, encrypt_batch_write_item, TableInfoCache
 )
diff --git a/src/dynamodb_encryption_sdk/encrypted/table.py b/src/dynamodb_encryption_sdk/encrypted/table.py
index 1e10973e..fa87d575 100644
--- a/src/dynamodb_encryption_sdk/encrypted/table.py
+++ b/src/dynamodb_encryption_sdk/encrypted/table.py
@@ -17,6 +17,12 @@
 from boto3.dynamodb.table import BatchWriter
 from boto3.resources.base import ServiceResource
 
+try:  # Python 3.5.0 and 3.5.1 have incompatible typing modules
+    from typing import Optional  # noqa pylint: disable=unused-import
+except ImportError:  # pragma: no cover
+    # We only actually need these imports when running the mypy checks
+    pass
+
 from dynamodb_encryption_sdk.internal.utils import (
     crypto_config_from_kwargs, crypto_config_from_table_info,
     decrypt_get_item, decrypt_multi_get, encrypt_put_item
diff --git a/src/dynamodb_encryption_sdk/internal/crypto/jce_bridge/primitives.py b/src/dynamodb_encryption_sdk/internal/crypto/jce_bridge/primitives.py
index 4adec1f7..9519cc86 100644
--- a/src/dynamodb_encryption_sdk/internal/crypto/jce_bridge/primitives.py
+++ b/src/dynamodb_encryption_sdk/internal/crypto/jce_bridge/primitives.py
@@ -23,7 +23,7 @@
 import six
 
 try:  # Python 3.5.0 and 3.5.1 have incompatible typing modules
-    from typing import Callable, Text  # noqa pylint: disable=unused-import
+    from typing import Any, Callable, Text  # noqa pylint: disable=unused-import
 except ImportError:  # pragma: no cover
     # We only actually need these imports when running the mypy checks
     pass
@@ -268,8 +268,10 @@ def __init__(
         self.java_name = java_name
         self.cipher = cipher
         attr.validate(self)
-        if hasattr(self, '__attrs_post_init__'):
-            self.__attrs_post_init__()
+        self.__attrs_post_init__()
+
+    def __attrs_post_init__(self):
+        """No-op stub to standardize API."""
 
     def validate_algorithm(self, algorithm):
         # type: (Text) -> None
diff --git a/src/dynamodb_encryption_sdk/internal/dynamodb_types.py b/src/dynamodb_encryption_sdk/internal/dynamodb_types.py
index abac1d3b..fd87ae92 100644
--- a/src/dynamodb_encryption_sdk/internal/dynamodb_types.py
+++ b/src/dynamodb_encryption_sdk/internal/dynamodb_types.py
@@ -1,14 +1,14 @@
 """Types used with mypy for DynamoDB items and attributes."""
 try:  # Python 3.5.0 and 3.5.1 have incompatible typing modules
-    from typing import Any, ByteString, Dict, List, Text, Union
+    from typing import Any, AnyStr, ByteString, Dict, List, Text
 
-    ATTRIBUTE = Any  # TODO: narrow this down
+    ATTRIBUTE = Dict[Text, Any]  # TODO: narrow this down
     ITEM = Dict[Text, ATTRIBUTE]
     RAW_ATTRIBUTE = ITEM
     NULL = bool  # DynamoDB TypeSerializer converts none to {'NULL': True}
     BOOLEAN = bool
     NUMBER = int  # TODO: This misses long on Python 2...figure out something for this
-    STRING = Union[Text, Text]  # TODO: can be unicode but should not be bytes
+    STRING = AnyStr  # TODO: can be unicode but should not be bytes
     BINARY = ByteString
     BINARY_ATTRIBUTE = Dict[Text, BINARY]
     SET = List  # DynamoDB TypeSerializer converts sets into lists
diff --git a/src/dynamodb_encryption_sdk/internal/formatting/deserialize/attribute.py b/src/dynamodb_encryption_sdk/internal/formatting/deserialize/attribute.py
index 6af16605..b4f1327c 100644
--- a/src/dynamodb_encryption_sdk/internal/formatting/deserialize/attribute.py
+++ b/src/dynamodb_encryption_sdk/internal/formatting/deserialize/attribute.py
@@ -18,7 +18,7 @@
 import struct
 
 try:  # Python 3.5.0 and 3.5.1 have incompatible typing modules
-    from typing import Callable, Dict, List, Union  # noqa pylint: disable=unused-import
+    from typing import Callable, Dict, List, Text, Union  # noqa pylint: disable=unused-import
     from dynamodb_encryption_sdk.internal import dynamodb_types  # noqa pylint: disable=unused-import,ungrouped-imports
 except ImportError:  # pragma: no cover
     # We only actually need these imports when running the mypy checks
@@ -52,7 +52,7 @@ def _transform_binary_value(value):
         return value
 
     def _deserialize_binary(stream):
-        # type: (io.BytesIO) -> Dict[str, bytes]
+        # type: (io.BytesIO) -> Dict[Text, bytes]
         """Deserializes a binary object.
 
         :param stream: Stream containing serialized object
@@ -72,7 +72,7 @@ def _transform_string_value(value):
         return codecs.decode(value, TEXT_ENCODING)
 
     def _deserialize_string(stream):
-        # type: (io.BytesIO) -> Dict[str, dynamodb_types.STRING]
+        # type: (io.BytesIO) -> Dict[Text, dynamodb_types.STRING]
         """Deserializes a string object.
 
         :param stream: Stream containing serialized object
@@ -94,7 +94,7 @@ def _transform_number_value(value):
         return '{0:f}'.format(decimal_value)
 
     def _deserialize_number(stream):
-        # type: (io.BytesIO) -> Dict[str, dynamodb_types.STRING]
+        # type: (io.BytesIO) -> Dict[Text, dynamodb_types.STRING]
         """Deserializes a number object.
 
         :param stream: Stream containing serialized object
@@ -110,7 +110,7 @@ def _deserialize_number(stream):
     }
 
     def _deserialize_boolean(stream):
-        # type: (io.BytesIO) -> Dict[str, dynamodb_types.BOOLEAN]
+        # type: (io.BytesIO) -> Dict[Text, dynamodb_types.BOOLEAN]
         """Deserializes a boolean object.
 
         :param stream: Stream containing serialized object
@@ -121,7 +121,7 @@ def _deserialize_boolean(stream):
         return {Tag.BOOLEAN.dynamodb_tag: _boolean_map[value]}
 
     def _deserialize_null(stream):  # we want a consistent API but don't use stream, so pylint: disable=unused-argument
-        # type: (io.BytesIO) -> Dict[str, dynamodb_types.BOOLEAN]
+        # type: (io.BytesIO) -> Dict[Text, dynamodb_types.BOOLEAN]
         """Deserializes a null object.
 
         :param stream: Stream containing serialized object
@@ -145,7 +145,7 @@ def _deserialize_set(stream, member_transform):
         ])
 
     def _deserialize_binary_set(stream):
-        # type: (io.BytesIO) -> Dict[str, dynamodb_types.SET[dynamodb_types.BINARY]]
+        # type: (io.BytesIO) -> Dict[Text, dynamodb_types.SET[dynamodb_types.BINARY]]
         """Deserializes a binary set object.
 
         :param stream: Stream containing serialized object
@@ -155,7 +155,7 @@ def _deserialize_binary_set(stream):
         return {Tag.BINARY_SET.dynamodb_tag: _deserialize_set(stream, _transform_binary_value)}
 
     def _deserialize_string_set(stream):
-        # type: (io.BytesIO) -> Dict[str, dynamodb_types.SET[dynamodb_types.STRING]]
+        # type: (io.BytesIO) -> Dict[Text, dynamodb_types.SET[dynamodb_types.STRING]]
         """Deserializes a string set object.
 
         :param stream: Stream containing serialized object
@@ -165,7 +165,7 @@ def _deserialize_string_set(stream):
         return {Tag.STRING_SET.dynamodb_tag: _deserialize_set(stream, _transform_string_value)}
 
     def _deserialize_number_set(stream):
-        # type: (io.BytesIO) -> Dict[str, dynamodb_types.SET[dynamodb_types.STRING]]
+        # type: (io.BytesIO) -> Dict[Text, dynamodb_types.SET[dynamodb_types.STRING]]
         """Deserializes a number set object.
 
         :param stream: Stream containing serialized object
@@ -175,7 +175,7 @@ def _deserialize_number_set(stream):
         return {Tag.NUMBER_SET.dynamodb_tag: _deserialize_set(stream, _transform_number_value)}
 
     def _deserialize_list(stream):
-        # type: (io.BytesIO) -> Dict[str, dynamodb_types.LIST]
+        # type: (io.BytesIO) -> Dict[Text, dynamodb_types.LIST]
         """Deserializes a list object.
 
         :param stream: Stream containing serialized object
@@ -189,7 +189,7 @@ def _deserialize_list(stream):
         ]}
 
     def _deserialize_map(stream):
-        # type: (io.BytesIO) -> Dict[str, dynamodb_types.MAP]
+        # type: (io.BytesIO) -> Dict[Text, dynamodb_types.MAP]
         """Deserializes a map object.
 
         :param stream: Stream containing serialized object
@@ -197,7 +197,7 @@ def _deserialize_map(stream):
         :rtype: dict
         """
         member_count = decode_length(stream)
-        members = {}
+        members = {}  # type: dynamodb_types.MAP
         for _ in range(member_count):
             key = _deserialize(stream)
             if Tag.STRING.dynamodb_tag not in key:
@@ -236,7 +236,7 @@ def _deserialize_function(tag):
             raise DeserializationError('Unsupported tag: "{}"'.format(tag))
 
     def _deserialize(stream):
-        # type: (io.BytesIO) -> Dict[str, dynamodb_types.RAW_ATTRIBUTE]
+        # type: (io.BytesIO) -> Dict[Text, dynamodb_types.RAW_ATTRIBUTE]
         """Deserializes a serialized object.
 
         :param stream: Stream containing serialized object
diff --git a/src/dynamodb_encryption_sdk/material_providers/__init__.py b/src/dynamodb_encryption_sdk/material_providers/__init__.py
index 82735d17..56799235 100644
--- a/src/dynamodb_encryption_sdk/material_providers/__init__.py
+++ b/src/dynamodb_encryption_sdk/material_providers/__init__.py
@@ -11,7 +11,7 @@
 # ANY KIND, either express or implied. See the License for the specific
 # language governing permissions and limitations under the License.
 """Cryptographic materials providers."""
-from dynamodb_encryption_sdk.materials import DecryptionMaterials, EncryptionMaterials  # noqa pylint: disable=unused-import
+from dynamodb_encryption_sdk.materials import CryptographicMaterials  # noqa pylint: disable=unused-import
 from dynamodb_encryption_sdk.structures import EncryptionContext  # noqa pylint: disable=unused-import
 
 __all__ = ('CryptographicMaterialsProvider',)
@@ -21,7 +21,7 @@ class CryptographicMaterialsProvider(object):
     """Base class for all cryptographic materials providers."""
 
     def decryption_materials(self, encryption_context):
-        # type: (EncryptionContext) -> DecryptionMaterials
+        # type: (EncryptionContext) -> CryptographicMaterials
         # pylint: disable=unused-argument,no-self-use
         """Return decryption materials.
 
@@ -32,7 +32,7 @@ def decryption_materials(self, encryption_context):
         raise AttributeError('No decryption materials available')
 
     def encryption_materials(self, encryption_context):
-        # type: (EncryptionContext) -> EncryptionMaterials
+        # type: (EncryptionContext) -> CryptographicMaterials
         # pylint: disable=unused-argument,no-self-use
         """Return encryption materials.
 
diff --git a/src/dynamodb_encryption_sdk/material_providers/aws_kms.py b/src/dynamodb_encryption_sdk/material_providers/aws_kms.py
index aebdb5f8..d2c8d81c 100644
--- a/src/dynamodb_encryption_sdk/material_providers/aws_kms.py
+++ b/src/dynamodb_encryption_sdk/material_providers/aws_kms.py
@@ -192,7 +192,8 @@ def __init__(
         if botocore_session is None:
             botocore_session = botocore.session.Session()
         if grant_tokens is None:
-            grant_tokens = ()
+            # reassignment confuses mypy
+            grant_tokens = ()  # type: ignore
         if material_description is None:
             material_description = {}
         if regional_clients is None:
@@ -292,7 +293,7 @@ def _validate_key_id(self, key_id, encryption_context):
         """
 
     def _attribute_to_value(self, attribute):
-        # type: (dynamodb_types.ITEM) -> str
+        # type: (dynamodb_types.ITEM) -> Text
         """Convert a DynamoDB attribute to a value that can be added to the KMS encryption context.
 
         :param dict attribute: Attribute to convert
@@ -307,7 +308,7 @@ def _attribute_to_value(self, attribute):
         raise ValueError('Attribute of type "{}" cannot be used in KMS encryption context.'.format(attribute_type))
 
     def _kms_encryption_context(self, encryption_context, encryption_description, signing_description):
-        # type: (EncryptionContext, Text, Text) -> Dict[str, str]
+        # type: (EncryptionContext, Text, Text) -> Dict[Text, Text]
         """Build the KMS encryption context from the encryption context and key descriptions.
 
         :param encryption_context: Encryption context providing information about request
@@ -346,7 +347,7 @@ def _kms_encryption_context(self, encryption_context, encryption_description, si
         return kms_encryption_context
 
     def _generate_initial_material(self, encryption_context):
-        # type: (EncryptionContext) -> (bytes, bytes)
+        # type: (EncryptionContext) -> Tuple[bytes, bytes]
         """Generate the initial cryptographic material for use with HKDF.
 
         :param encryption_context: Encryption context providing information about request
diff --git a/src/dynamodb_encryption_sdk/material_providers/static.py b/src/dynamodb_encryption_sdk/material_providers/static.py
index 8f903dd0..f629e333 100644
--- a/src/dynamodb_encryption_sdk/material_providers/static.py
+++ b/src/dynamodb_encryption_sdk/material_providers/static.py
@@ -13,6 +13,13 @@
 """Cryptographic materials provider for use with pre-configured encryption and decryption materials."""
 import attr
 
+try:  # Python 3.5.0 and 3.5.1 have incompatible typing modules
+    from typing import Optional  # noqa pylint: disable=unused-import
+except ImportError:  # pragma: no cover
+    # We only actually need these imports when running the mypy checks
+    pass
+
+from dynamodb_encryption_sdk.materials import CryptographicMaterials  # noqa pylint: disable=unused-import
 from dynamodb_encryption_sdk.materials import DecryptionMaterials, EncryptionMaterials
 from dynamodb_encryption_sdk.structures import EncryptionContext  # noqa pylint: disable=unused-import
 from . import CryptographicMaterialsProvider
@@ -54,7 +61,7 @@ def __init__(
         attr.validate(self)
 
     def decryption_materials(self, encryption_context):
-        # type: (EncryptionContext) -> DecryptionMaterials
+        # type: (EncryptionContext) -> CryptographicMaterials
         """Return the static decryption materials.
 
         :param encryption_context: Encryption context for request (not used by ``StaticCryptographicMaterialsProvider``)
@@ -67,7 +74,7 @@ def decryption_materials(self, encryption_context):
         return self._decryption_materials
 
     def encryption_materials(self, encryption_context):
-        # type: (EncryptionContext) -> EncryptionMaterials
+        # type: (EncryptionContext) -> CryptographicMaterials
         """Return the static encryption materials.
 
         :param encryption_context: Encryption context for request (not used by ``StaticCryptographicMaterialsProvider``)
diff --git a/src/dynamodb_encryption_sdk/material_providers/wrapped.py b/src/dynamodb_encryption_sdk/material_providers/wrapped.py
index 9c038834..430505f9 100644
--- a/src/dynamodb_encryption_sdk/material_providers/wrapped.py
+++ b/src/dynamodb_encryption_sdk/material_providers/wrapped.py
@@ -13,6 +13,12 @@
 """Cryptographic materials provider to use ephemeral content encryption keys wrapped by delegated keys."""
 import attr
 
+try:  # Python 3.5.0 and 3.5.1 have incompatible typing modules
+    from typing import Optional  # noqa pylint: disable=unused-import
+except ImportError:  # pragma: no cover
+    # We only actually need these imports when running the mypy checks
+    pass
+
 from dynamodb_encryption_sdk.delegated_keys import DelegatedKey
 from dynamodb_encryption_sdk.exceptions import UnwrappingError, WrappingError
 from dynamodb_encryption_sdk.materials.wrapped import WrappedCryptographicMaterials
diff --git a/src/dynamodb_encryption_sdk/materials/raw.py b/src/dynamodb_encryption_sdk/materials/raw.py
index 3cf98ae8..fa982263 100644
--- a/src/dynamodb_encryption_sdk/materials/raw.py
+++ b/src/dynamodb_encryption_sdk/materials/raw.py
@@ -106,7 +106,7 @@ def material_description(self):
 
     @property
     def signing_key(self):
-        # type: () -> Dict[Text, Text]
+        # type: () -> DelegatedKey
         """Delegated key used for calculating digital signatures.
 
         :returns: Signing key
@@ -116,7 +116,7 @@ def signing_key(self):
 
     @property
     def encryption_key(self):
-        # type: () -> Dict[Text, Text]
+        # type: () -> DelegatedKey
         """Delegated key used for encrypting attributes.
 
         :returns: Encryption key
@@ -194,7 +194,7 @@ def material_description(self):
 
     @property
     def verification_key(self):
-        # type: () -> Dict[Text, Text]
+        # type: () -> DelegatedKey
         """Delegated key used for verifying digital signatures.
 
         :returns: Verification key
@@ -204,7 +204,7 @@ def verification_key(self):
 
     @property
     def decryption_key(self):
-        # type: () -> Dict[Text, Text]
+        # type: () -> DelegatedKey
         """Delegated key used for decrypting attributes.
 
         :returns: Decryption key
diff --git a/src/dynamodb_encryption_sdk/structures.py b/src/dynamodb_encryption_sdk/structures.py
index b69e2904..85382f82 100644
--- a/src/dynamodb_encryption_sdk/structures.py
+++ b/src/dynamodb_encryption_sdk/structures.py
@@ -17,7 +17,7 @@
 import six
 
 try:  # Python 3.5.0 and 3.5.1 have incompatible typing modules
-    from typing import Dict, Iterables, Optional, Set, Text  # noqa pylint: disable=unused-import
+    from typing import Dict, Iterable, Optional, Set, Text  # noqa pylint: disable=unused-import
 except ImportError:  # pragma: no cover
     # We only actually need these imports when running the mypy checks
     pass
@@ -86,7 +86,7 @@ def __init__(
             table_name=None,  # type: Optional[Text]
             partition_key_name=None,  # type: Optional[Text]
             sort_key_name=None,  # type: Optional[Text]
-            attributes=None,  # type: Optional[Dict[Text, Dict]
+            attributes=None,  # type: Optional[Dict[Text, Dict]]
             material_description=None  # type: Optional[Dict[Text, Text]]
     ):
         # type: (...) -> None