diff --git a/b2sdk/raw_api.py b/b2sdk/raw_api.py
index 19d4fabf7..08afaeb2c 100644
--- a/b2sdk/raw_api.py
+++ b/b2sdk/raw_api.py
@@ -830,6 +830,7 @@ def copy_part(
             _add_range_header(range_dict, bytes_range)
             kwargs['range'] = range_dict['Range']
         if destination_server_side_encryption is not None:
+            assert destination_server_side_encryption.mode != EncryptionMode.SSE_B2
             kwargs['destinationServerSideEncryption'
                   ] = destination_server_side_encryption.as_value_dict()
         return self._post_json(
@@ -1100,10 +1101,14 @@ def test_raw_api_helper(raw_api):
         io.BytesIO(part_contents)
     )
 
+    # b2_copy_part
+    print('b2_copy_part')
+    raw_api.copy_part(api_url, account_auth_token, file_id, large_file_id, 2, (0, 5))
+
     # b2_list_parts
     print('b2_list_parts')
     parts_response = raw_api.list_parts(api_url, account_auth_token, large_file_id, 1, 100)
-    assert [1] == [part['partNumber'] for part in parts_response['parts']]
+    assert [1, 2] == [part['partNumber'] for part in parts_response['parts']]
 
     # b2_list_unfinished_large_files
     unfinished_list = raw_api.list_unfinished_large_files(api_url, account_auth_token, bucket_id)
@@ -1111,14 +1116,13 @@ def test_raw_api_helper(raw_api):
     assert file_info == unfinished_list['files'][0]['fileInfo']
 
     # b2_finish_large_file
-    # We don't upload enough data to actually finish on, so we'll just
-    # check that the right error is returned.
     print('b2_finish_large_file')
     try:
         raw_api.finish_large_file(api_url, account_auth_token, large_file_id, [part_sha1])
         raise Exception('finish should have failed')
     except Exception as e:
         assert 'large files must have at least 2 parts' in str(e)
+    # TODO: make another attempt to finish but this time successfully
 
     # b2_update_bucket
     print('b2_update_bucket')
diff --git a/b2sdk/raw_simulator.py b/b2sdk/raw_simulator.py
index 44bb5fc5e..e57cccef0 100644
--- a/b2sdk/raw_simulator.py
+++ b/b2sdk/raw_simulator.py
@@ -1125,6 +1125,10 @@ def copy_part(
         bytes_range=None,
         destination_server_side_encryption: Optional[EncryptionSetting] = None,
     ):
+        if destination_server_side_encryption is not None and destination_server_side_encryption.mode == EncryptionMode.SSE_B2:
+            raise ValueError(
+                'unsupported sse mode for copy_part!'
+            )  # SSE-B2 is only to be marked in b2_start_large_file
         src_bucket_id = self.file_id_to_bucket_id[source_file_id]
         src_bucket = self._get_bucket_by_id(src_bucket_id)
         dest_bucket_id = self.file_id_to_bucket_id[large_file_id]
diff --git a/b2sdk/transfer/emerge/executor.py b/b2sdk/transfer/emerge/executor.py
index 3f30f66d2..082552bca 100644
--- a/b2sdk/transfer/emerge/executor.py
+++ b/b2sdk/transfer/emerge/executor.py
@@ -395,7 +395,6 @@ def __init__(
         large_file_id,
         large_file_upload_state,
         finished_parts=None,
-        destination_encryption: Optional[EncryptionSetting] = None,
     ):
         super(LargeFileEmergeExecutionStepFactory, self).__init__(emerge_execution, emerge_part)
         self.part_number = part_number
@@ -421,7 +420,7 @@ def create_upload_execution_step(self, stream_opener, stream_length=None, stream
             self.large_file_upload_state,
             stream_length=stream_length,
             stream_sha1=stream_sha1,
-            finished_parts=self.finished_parts
+            finished_parts=self.finished_parts,
         )
 
 
diff --git a/b2sdk/transfer/outbound/copy_manager.py b/b2sdk/transfer/outbound/copy_manager.py
index a6fabed39..d1eb4f4e8 100644
--- a/b2sdk/transfer/outbound/copy_manager.py
+++ b/b2sdk/transfer/outbound/copy_manager.py
@@ -131,6 +131,10 @@ def _copy_part(
             EncryptionMode.SSE_B2,
         )
 
+        # b2_copy_part doesn't need SSE-B2. Large file encryption is decided on b2_start_large_file.
+        if destination_encryption is not None and destination_encryption.mode == EncryptionMode.SSE_B2:
+            destination_encryption = None
+
         # Check if this part was uploaded before
         if finished_parts is not None and part_number in finished_parts:
             # Report this part finished
diff --git a/b2sdk/transfer/outbound/upload_manager.py b/b2sdk/transfer/outbound/upload_manager.py
index 496bcb1d1..5e67e803c 100644
--- a/b2sdk/transfer/outbound/upload_manager.py
+++ b/b2sdk/transfer/outbound/upload_manager.py
@@ -137,6 +137,11 @@ def _upload_part(
         :param b2sdk.v1.EncryptionSetting encryption: encryption setting (``None`` if unknown)
         """
         assert encryption is None or encryption.mode in (EncryptionMode.SSE_B2,)
+
+        # b2_upload_part doesn't need SSE-B2. Large file encryption is decided on b2_start_large_file.
+        if encryption is not None and encryption.mode == EncryptionMode.SSE_B2:
+            encryption = None
+
         # Check if this part was uploaded before
         if finished_parts is not None and part_number in finished_parts:
             # Report this part finished