diff --git a/pyairtable/api/table.py b/pyairtable/api/table.py
index ceba27b6..e9faafcf 100644
--- a/pyairtable/api/table.py
+++ b/pyairtable/api/table.py
@@ -5,17 +5,7 @@
 import urllib.parse
 import warnings
 from pathlib import Path
-from typing import (
-    Any,
-    BinaryIO,
-    Dict,
-    Iterable,
-    Iterator,
-    List,
-    Optional,
-    Union,
-    overload,
-)
+from typing import Any, Dict, Iterable, Iterator, List, Optional, Union, overload
 
 import pyairtable.models
 from pyairtable.api.retrying import Retry
@@ -711,7 +701,7 @@ def upload_attachment(
         record_id: RecordId,
         field: str,
         filename: Union[str, Path],
-        content: Optional[bytes] = None,
+        content: Optional[Union[str, bytes]] = None,
         content_type: Optional[str] = None,
     ) -> UploadAttachmentResultDict:
         """ """
@@ -730,6 +720,7 @@ def upload_attachment(
 
         # TODO: figure out how to handle the atypical subdomain in a more graceful fashion
         url = f"https://content.airtable.com/v0/{self.base.id}/{record_id}/{field}/uploadAttachment"
+        content = content.encode() if isinstance(content, str) else content
         payload = {
             "contentType": content_type,
             "filename": filename,
diff --git a/pyairtable/orm/lists.py b/pyairtable/orm/lists.py
index 97623b39..701da08a 100644
--- a/pyairtable/orm/lists.py
+++ b/pyairtable/orm/lists.py
@@ -101,7 +101,7 @@ class AttachmentsList(ChangeTrackingList[AttachmentDict]):
     def upload(
         self,
         filename: Union[str, Path],
-        content: Optional[bytes] = None,
+        content: Optional[Union[str, bytes]] = None,
         content_type: Optional[str] = None,
     ) -> None:
         """
diff --git a/tests/test_api_table.py b/tests/test_api_table.py
index ef9f5dca..4a4f9d4f 100644
--- a/tests/test_api_table.py
+++ b/tests/test_api_table.py
@@ -618,11 +618,12 @@ def mock_upload_attachment(requests_mock, table):
     )
 
 
-def test_upload_attachment(mock_upload_attachment, table):
+@pytest.mark.parametrize("content", [b"Hello, World!", "Hello, World!"])
+def test_upload_attachment(mock_upload_attachment, table, content):
     """
     Test that we can upload an attachment to a record.
     """
-    table.upload_attachment(RECORD_ID, FIELD_ID, "sample.txt", b"Hello, World!")
+    table.upload_attachment(RECORD_ID, FIELD_ID, "sample.txt", content)
     assert mock_upload_attachment.last_request.json() == {
         "contentType": "text/plain",
         "file": "SGVsbG8sIFdvcmxkIQ==\n",  # base64 encoded "Hello, World!"
@@ -630,7 +631,7 @@ def test_upload_attachment(mock_upload_attachment, table):
     }
 
 
-def test_upload_attachment__no_content(mock_upload_attachment, table, tmp_path):
+def test_upload_attachment__no_content_type(mock_upload_attachment, table, tmp_path):
     """
     Test that we can upload an attachment to a record.
     """
diff --git a/tests/test_orm_lists.py b/tests/test_orm_lists.py
index 244df3bc..8d867761 100644
--- a/tests/test_orm_lists.py
+++ b/tests/test_orm_lists.py
@@ -37,21 +37,23 @@ def mock_upload():
         yield m
 
 
-def test_attachment_upload(mock_upload, tmp_path):
+@pytest.mark.parametrize("content", [b"Hello, world!", "Hello, world!"])
+def test_attachment_upload(mock_upload, tmp_path, content):
     """
     Test that we can add an attachment to a record.
     """
-    tmp_file = tmp_path / "a.txt"
-    tmp_file.write_text("Hello, world!")
+    fp = tmp_path / "a.txt"
+    writer = fp.write_text if isinstance(content, str) else fp.write_bytes
+    writer(content)
 
     record = fake_record()
     instance = Fake.from_record(record)
-    instance.attachments.upload(tmp_file)
+    instance.attachments.upload(fp)
 
     mock_upload.assert_called_once_with(
         record["id"],
         "Files",
-        filename=tmp_file,
+        filename=fp,
         content=None,
         content_type=None,
     )