diff --git a/src/ocrmypdf/api.py b/src/ocrmypdf/api.py
index 700a3a98..69de7fbd 100644
--- a/src/ocrmypdf/api.py
+++ b/src/ocrmypdf/api.py
@@ -209,6 +209,9 @@ def create_options(
         cmdline.append('stream://output_file')
     else:
         cmdline.append(os.fspath(output_file))
+    if 'sidecar' in kwargs and isinstance(kwargs['sidecar'], BinaryIO | IOBase):
+        cmdline.append('--sidecar')
+        cmdline.append('stream://sidecar')
 
     parser.enable_api_mode()
     options = parser.parse_args(cmdline)
@@ -219,6 +222,8 @@ def create_options(
         options.input_file = input_file
     if options.output_file == 'stream://output_file':
         options.output_file = output_file
+    if options.sidecar == 'stream://sidecar':
+        options.sidecar = kwargs['sidecar']
 
     return options
 
@@ -230,7 +235,7 @@ def ocr(  # noqa: D417
     language: Iterable[str] | None = None,
     image_dpi: int | None = None,
     output_type: str | None = None,
-    sidecar: StrPath | None = None,
+    sidecar: PathOrIO | None = None,
     jobs: int | None = None,
     use_threads: bool | None = None,
     title: str | None = None,
diff --git a/tests/test_api.py b/tests/test_api.py
index 540d4ac0..f5eea148 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -29,6 +29,18 @@ def test_stream_api(resources: Path):
     assert b'%PDF' in out.read(1024)
 
 
+def test_sidecar_stringio(resources: Path, outdir: Path, outpdf: Path):
+    s = BytesIO()
+    ocrmypdf.ocr(
+        resources / 'ccitt.pdf',
+        outpdf,
+        plugins=['tests/plugins/tesseract_cache.py'],
+        sidecar=s
+    )
+    s.seek(0)
+    assert b'the' in s.getvalue()
+
+
 def test_hocr_api_multipage(resources: Path, outdir: Path, outpdf: Path):
     ocrmypdf.api._pdf_to_hocr(
         resources / 'multipage.pdf',
@@ -62,3 +74,4 @@ def test_hocr_to_pdf_api(resources: Path, outdir: Path, outpdf: Path):
 
     text = extract_text(outpdf)
     assert 'hocr' in text and 'the' not in text
+