diff --git a/src/aws_encryption_sdk/key_providers/kms.py b/src/aws_encryption_sdk/key_providers/kms.py
index 45402077d..b34e0b8fc 100644
--- a/src/aws_encryption_sdk/key_providers/kms.py
+++ b/src/aws_encryption_sdk/key_providers/kms.py
@@ -199,10 +199,10 @@ def _generate_data_key(self, algorithm, encryption_context=None):
             # //# ciphertext for the encrypted data key in the output.
             ciphertext = response["CiphertextBlob"]
             key_id = response["KeyId"]
-        except (ClientError, KeyError):
+        except (ClientError, KeyError) as error:
             error_message = "Master Key {key_id} unable to generate data key".format(key_id=self._key_id)
             _LOGGER.exception(error_message)
-            raise GenerateKeyError(error_message)
+            raise GenerateKeyError(error_message) from error
 
         # //= compliance/framework/aws-kms/aws-kms-mrk-aware-master-key.txt#2.10
         # //# The response's "KeyId" MUST be valid.
@@ -242,10 +242,10 @@ def _encrypt_data_key(self, data_key, algorithm, encryption_context=None):
             # //# encrypted data key.
             ciphertext = response["CiphertextBlob"]
             key_id = response["KeyId"]
-        except (ClientError, KeyError):
+        except (ClientError, KeyError) as error:
             error_message = "Master Key {key_id} unable to encrypt data key".format(key_id=self._key_id)
             _LOGGER.exception(error_message)
-            raise EncryptKeyError(error_message)
+            raise EncryptKeyError(error_message) from error
 
         # //= compliance/framework/aws-kms/aws-kms-mrk-aware-master-key.txt#2.11
         # //# The AWS KMS Encrypt response MUST contain a valid "KeyId".
@@ -315,10 +315,10 @@ def _decrypt_data_key(self, encrypted_data_key, algorithm, encryption_context=No
                 )
                 raise DecryptKeyError(error_message)
 
-        except (ClientError, KeyError):
+        except (ClientError, KeyError) as error:
             error_message = "Master Key {key_id} unable to decrypt data key".format(key_id=self._key_id)
             _LOGGER.exception(error_message)
-            raise DecryptKeyError(error_message)
+            raise DecryptKeyError(error_message) from error
         return DataKey(
             key_provider=self.key_provider, data_key=plaintext, encrypted_data_key=encrypted_data_key.encrypted_data_key
         )
diff --git a/test/unit/test_providers_kms_master_key.py b/test/unit/test_providers_kms_master_key.py
index 01a87d4fd..c38a0c853 100644
--- a/test/unit/test_providers_kms_master_key.py
+++ b/test/unit/test_providers_kms_master_key.py
@@ -229,6 +229,21 @@ def test_generate_data_key_unsuccessful_clienterror(self, config_class, key_clas
             test._generate_data_key(self.mock_algorithm)
         excinfo.match("Master Key .* unable to generate data key")
 
+    @pytest.mark.parametrize(
+        "config_class, key_class",
+        [(KMSMasterKeyConfig, KMSMasterKey), (MRKAwareKMSMasterKeyConfig, MRKAwareKMSMasterKey)],
+    )
+    @pytest.mark.parametrize("key_id", [VALUES["mrk_arn_region1"], VALUES["arn"]])
+    def test_generate_data_key_clienterror_preserves_cause(self, config_class, key_class, key_id):
+        """The original KMS error must be chained as __cause__ (see GitHub issue #774)."""
+        root_error = ClientError({"Error": {}}, "This is an error!")
+        self.mock_client.generate_data_key.side_effect = root_error
+        config = config_class(key_id=key_id, client=self.mock_client)
+        test = key_class(config=config)
+        with pytest.raises(GenerateKeyError) as excinfo:
+            test._generate_data_key(self.mock_algorithm)
+        assert excinfo.value.__cause__ is root_error
+
     @pytest.mark.parametrize(
         "config_class, key_class",
         [(KMSMasterKeyConfig, KMSMasterKey), (MRKAwareKMSMasterKeyConfig, MRKAwareKMSMasterKey)],
@@ -344,6 +359,21 @@ def test_encrypt_data_key_unsuccessful_clienterror(self, config_class, key_class
             test._encrypt_data_key(self.mock_data_key, self.mock_algorithm)
         excinfo.match("Master Key .* unable to encrypt data key")
 
+    @pytest.mark.parametrize(
+        "config_class, key_class",
+        [(KMSMasterKeyConfig, KMSMasterKey), (MRKAwareKMSMasterKeyConfig, MRKAwareKMSMasterKey)],
+    )
+    @pytest.mark.parametrize("key_id", [VALUES["mrk_arn_region1"], VALUES["arn"]])
+    def test_encrypt_data_key_clienterror_preserves_cause(self, config_class, key_class, key_id):
+        """The original KMS error must be chained as __cause__ (see GitHub issue #774)."""
+        root_error = ClientError({"Error": {}}, "This is an error!")
+        self.mock_client.encrypt.side_effect = root_error
+        config = config_class(key_id=key_id, client=self.mock_client)
+        test = key_class(config=config)
+        with pytest.raises(EncryptKeyError) as excinfo:
+            test._encrypt_data_key(self.mock_data_key, self.mock_algorithm)
+        assert excinfo.value.__cause__ is root_error
+
     @pytest.mark.parametrize(
         "config_class, key_class",
         [(KMSMasterKeyConfig, KMSMasterKey), (MRKAwareKMSMasterKeyConfig, MRKAwareKMSMasterKey)],
@@ -498,6 +528,23 @@ def test_decrypt_data_key_unsuccessful_clienterror(self, config_class, key_class
             test._decrypt_data_key(encrypted_data_key=self.mock_encrypted_data_key, algorithm=sentinel.algorithm)
         excinfo.match("Master Key .* unable to decrypt data key")
 
+    @pytest.mark.parametrize(
+        "config_class, key_class",
+        [(KMSMasterKeyConfig, KMSMasterKey), (MRKAwareKMSMasterKeyConfig, MRKAwareKMSMasterKey)],
+    )
+    @pytest.mark.parametrize("key_id", [VALUES["mrk_arn_region1"], VALUES["arn"]])
+    def test_decrypt_data_key_clienterror_preserves_cause(self, config_class, key_class, key_id):
+        """The original KMS error must be chained as __cause__ (see GitHub issue #774)."""
+        root_error = ClientError({"Error": {}}, "This is an error!")
+        self.mock_client.decrypt.side_effect = root_error
+        config = config_class(key_id=key_id, client=self.mock_client)
+        test = key_class(config=config)
+        self.mock_encrypted_data_key.key_provider.key_info = key_id
+        self.mock_client.decrypt.return_value["KeyId"] = key_id.decode("ascii")
+        with pytest.raises(DecryptKeyError) as excinfo:
+            test._decrypt_data_key(encrypted_data_key=self.mock_encrypted_data_key, algorithm=sentinel.algorithm)
+        assert excinfo.value.__cause__ is root_error
+
     @pytest.mark.parametrize(
         "config_class, key_class",
         [(KMSMasterKeyConfig, KMSMasterKey), (MRKAwareKMSMasterKeyConfig, MRKAwareKMSMasterKey)],