diff --git a/genanki/note.py b/genanki/note.py
index 0ffcd98..42609be 100644
--- a/genanki/note.py
+++ b/genanki/note.py
@@ -47,7 +47,7 @@ class _TagList(list):
 
 
 class Note:
-  _INVALID_HTML_TAG_RE = re.compile(r'<(?!/?[a-z0-9]+(?: .*|/?)>)(?:.|\n)*?>')
+  _INVALID_HTML_TAG_RE = re.compile(r'<(?!/?[a-zA-Z0-9]+(?: .*|/?)>)(?:.|\n)*?>')
 
   def __init__(self, model=None, fields=None, sort_field=None, tags=None, guid=None, due=0):
     self.model = model

diff --git a/tests/test_note.py b/tests/test_note.py
index ede19f3..f654e30 100644
--- a/tests/test_note.py
+++ b/tests/test_note.py
@@ -172,6 +172,9 @@ class TestFindInvalidHtmlTagsInField:
 
   def test_ok_attrs(self):
     assert genanki.Note._find_invalid_html_tags_in_field('<h1 style="color: red">STOP</h1>') == []
+    
+  def test_ok_uppercase(self):
+    assert genanki.Note._find_invalid_html_tags_in_field('<TD></Td>') == []
 
   def test_ng_empty(self):
     assert genanki.Note._find_invalid_html_tags_in_field(' hello <> goodbye') == ['<>']

HTML tags are not case sensitive
`_INVALID_HTML_TAG_RE` is case sensitive, so I'm getting false positive warnings on tags like `<TABLE>, `<TD>`, etc.
tests/test_note.py::TestFindInvalidHtmlTagsInField::test_ok_uppercase
tests/test_note.py::TestTags::test_init tests/test_note.py::TestTags::test_assign tests/test_note.py::TestTags::test_assign_element tests/test_note.py::TestTags::test_assign_slice tests/test_note.py::TestTags::test_append tests/test_note.py::TestTags::test_extend tests/test_note.py::TestTags::test_insert tests/test_note.py::test_num_fields_equals_model_ok tests/test_note.py::test_num_fields_less_than_model_raises tests/test_note.py::test_num_fields_more_than_model_raises tests/test_note.py::TestFindInvalidHtmlTagsInField::test_ok tests/test_note.py::TestFindInvalidHtmlTagsInField::test_ok_with_space tests/test_note.py::TestFindInvalidHtmlTagsInField::test_ok_multiple tests/test_note.py::TestFindInvalidHtmlTagsInField::test_ok_br tests/test_note.py::TestFindInvalidHtmlTagsInField::test_ok_br2 tests/test_note.py::TestFindInvalidHtmlTagsInField::test_ok_br3 tests/test_note.py::TestFindInvalidHtmlTagsInField::test_ok_attrs tests/test_note.py::TestFindInvalidHtmlTagsInField::test_ng_empty tests/test_note.py::TestFindInvalidHtmlTagsInField::test_ng_empty_space tests/test_note.py::TestFindInvalidHtmlTagsInField::test_ng_invalid_characters tests/test_note.py::TestFindInvalidHtmlTagsInField::test_ng_invalid_characters_end tests/test_note.py::TestFindInvalidHtmlTagsInField::test_ng_issue_28 tests/test_note.py::test_warns_on_invalid_html_tags