diff --git a/Lib/test/test_xml_etree.py b/Lib/test/test_xml_etree.py
index 0c944516ae115f1..2af2d1fd64520b1 100644
--- a/Lib/test/test_xml_etree.py
+++ b/Lib/test/test_xml_etree.py
@@ -933,6 +933,7 @@ def test_tostring_xml_declaration_cases(self):
(b"\n"
b"\xf8", 'ISO-8859-1', None),
('ø', 'unicode', None),
+ (b"\xef\xbb\xbf\xc3\xb8", 'utf-8-sig', None),
# ... xml_declaration = False
(b"ø", None, False),
@@ -940,6 +941,7 @@ def test_tostring_xml_declaration_cases(self):
(b"ø", 'US-ASCII', False),
(b"\xf8", 'ISO-8859-1', False),
("ø", 'unicode', False),
+ (b"\xef\xbb\xbf\xc3\xb8", 'utf-8-sig', False),
# ... xml_declaration = True
(b"\n"
@@ -952,6 +954,8 @@ def test_tostring_xml_declaration_cases(self):
b"\xf8", 'ISO-8859-1', True),
("\n"
"ø", 'unicode', True),
+ (b"\xef\xbb\xbf\n"
+ b"\xc3\xb8", 'utf-8-sig', True),
]
for expected_retval, encoding, xml_declaration in TESTCASES:
diff --git a/Lib/xml/etree/ElementTree.py b/Lib/xml/etree/ElementTree.py
index 7708d38b7759cb1..951540eb9f45e90 100644
--- a/Lib/xml/etree/ElementTree.py
+++ b/Lib/xml/etree/ElementTree.py
@@ -732,6 +732,8 @@ def write(self, file_or_filename,
if not encoding:
encoding = "us-ascii"
with _get_writer(file_or_filename, encoding) as (write, declared_encoding):
+ if declared_encoding.lower() == "utf-8-sig":
+ declared_encoding = "utf-8"
if method == "xml" and (xml_declaration or
(xml_declaration is None and
encoding.lower() != "unicode" and
diff --git a/Misc/NEWS.d/next/Library/2026-08-12-22-15-00.gh-issue-90756.Qn7dLm.rst b/Misc/NEWS.d/next/Library/2026-08-12-22-15-00.gh-issue-90756.Qn7dLm.rst
new file mode 100644
index 000000000000000..dc15291d54a4ea4
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-08-12-22-15-00.gh-issue-90756.Qn7dLm.rst
@@ -0,0 +1,2 @@
+:meth:`xml.etree.ElementTree.ElementTree.write` now treats the ``utf-8-sig``
+encoding as ``utf-8`` in the XML declaration.