diff --git a/Lib/html/parser.py b/Lib/html/parser.py
index e50620de800..80fb8c3f929 100644
--- a/Lib/html/parser.py
+++ b/Lib/html/parser.py
@@ -24,6 +24,7 @@ incomplete = re.compile('&[a-zA-Z#]')
 
 entityref = re.compile('&([a-zA-Z][-.a-zA-Z0-9]*)[^a-zA-Z0-9]')
 charref = re.compile('&#(?:[0-9]+|[xX][0-9a-fA-F]+)[^0-9a-fA-F]')
+incomplete_charref = re.compile('&#(?:[0-9]|[xX][0-9a-fA-F])')
 attr_charref = re.compile(r'&(#[0-9]+|#[xX][0-9a-fA-F]+|[a-zA-Z][a-zA-Z0-9]*)[;=]?')
 
 starttagopen = re.compile('<[a-zA-Z]')
@@ -304,10 +305,20 @@ class HTMLParser(_markupbase.ParserBase):
                         k = k - 1
                     i = self.updatepos(i, k)
                     continue
+                match = incomplete_charref.match(rawdata, i)
+                if match:
+                    if end:
+                        self.handle_charref(rawdata[i+2:])
+                        i = self.updatepos(i, n)
+                        break
+                    # incomplete
+                    break
+                elif i + 3 < n:  # larger than "&#x"
+                    # not the end of the buffer, and can't be confused
+                    # with some other construct
+                    self.handle_data("&#")
+                    i = self.updatepos(i, i + 2)
                 else:
-                    if ";" in rawdata[i:]:  # bail by consuming &#
-                        self.handle_data(rawdata[i:i+2])
-                        i = self.updatepos(i, i+2)
                     break
             elif startswith('&', i):
                 match = entityref.match(rawdata, i)
@@ -321,15 +332,13 @@ class HTMLParser(_markupbase.ParserBase):
                     continue
                 match = incomplete.match(rawdata, i)
                 if match:
-                    # match.group() will contain at least 2 chars
-                    if end and match.group() == rawdata[i:]:
-                        k = match.end()
-                        if k <= i:
-                            k = n
-                        i = self.updatepos(i, i + 1)
+                    if end:
+                        self.handle_entityref(rawdata[i+1:])
+                        i = self.updatepos(i, n)
+                        break
                     # incomplete
                     break
-                elif (i + 1) < n:
+                elif i + 1 < n:
                     # not the end of the buffer, and can't be confused
                     # with some other construct
                     self.handle_data("&")
diff --git a/Lib/test/test_htmlparser.py b/Lib/test/test_htmlparser.py
index 19dde9362a4..e4eff1ea17a 100644
--- a/Lib/test/test_htmlparser.py
+++ b/Lib/test/test_htmlparser.py
@@ -109,12 +109,13 @@ class EventCollectorNoNormalize(EventCollector):
 
 class TestCaseBase(unittest.TestCase):
 
-    def get_collector(self):
-        return EventCollector(convert_charrefs=False)
+    def get_collector(self, convert_charrefs=False):
+        return EventCollector(convert_charrefs=convert_charrefs)
 
-    def _run_check(self, source, expected_events, collector=None):
+    def _run_check(self, source, expected_events,
+                   *, collector=None, convert_charrefs=False):
         if collector is None:
-            collector = self.get_collector()
+            collector = self.get_collector(convert_charrefs=convert_charrefs)
         parser = collector
         for s in source:
             parser.feed(s)
@@ -128,7 +129,7 @@ class TestCaseBase(unittest.TestCase):
 
     def _run_check_extra(self, source, events):
         self._run_check(source, events,
-                        EventCollectorExtra(convert_charrefs=False))
+            collector=EventCollectorExtra(convert_charrefs=False))
 
 
 class HTMLParserTestCase(TestCaseBase):
@@ -187,10 +188,87 @@ text
         ])
 
     def test_unclosed_entityref(self):
-        self._run_check("&entityref foo", [
-            ("entityref", "entityref"),
-            ("data", " foo"),
-            ])
+        self._run_check('&gt &lt;', [('entityref', 'gt'), ('data', ' '), ('entityref', 'lt')],
+                        convert_charrefs=False)
+        self._run_check('&gt &lt;', [('data', '> <')], convert_charrefs=True)
+
+        self._run_check('&undefined &lt;',
+                        [('entityref', 'undefined'), ('data', ' '), ('entityref', 'lt')],
+                        convert_charrefs=False)
+        self._run_check('&undefined &lt;', [('data', '&undefined <')],
+                        convert_charrefs=True)
+
+        self._run_check('&gtundefined &lt;',
+                        [('entityref', 'gtundefined'), ('data', ' '), ('entityref', 'lt')],
+                        convert_charrefs=False)
+        self._run_check('&gtundefined &lt;', [('data', '>undefined <')],
+                        convert_charrefs=True)
+
+        self._run_check('& &lt;', [('data', '& '), ('entityref', 'lt')],
+                        convert_charrefs=False)
+        self._run_check('& &lt;', [('data', '& <')], convert_charrefs=True)
+
+    def test_eof_in_entityref(self):
+        self._run_check('&gt', [('entityref', 'gt')], convert_charrefs=False)
+        self._run_check('&gt', [('data', '>')], convert_charrefs=True)
+
+        self._run_check('&g', [('entityref', 'g')], convert_charrefs=False)
+        self._run_check('&g', [('data', '&g')], convert_charrefs=True)
+
+        self._run_check('&undefined', [('entityref', 'undefined')],
+                        convert_charrefs=False)
+        self._run_check('&undefined', [('data', '&undefined')],
+                        convert_charrefs=True)
+
+        self._run_check('&gtundefined', [('entityref', 'gtundefined')],
+                        convert_charrefs=False)
+        self._run_check('&gtundefined', [('data', '>undefined')],
+                        convert_charrefs=True)
+
+        self._run_check('&', [('data', '&')], convert_charrefs=False)
+        self._run_check('&', [('data', '&')], convert_charrefs=True)
+
+    def test_unclosed_charref(self):
+        self._run_check('&#123 &lt;', [('charref', '123'), ('data', ' '), ('entityref', 'lt')],
+                        convert_charrefs=False)
+        self._run_check('&#123 &lt;', [('data', '{ <')], convert_charrefs=True)
+        self._run_check('&#xab &lt;', [('charref', 'xab'), ('data', ' '), ('entityref', 'lt')],
+                        convert_charrefs=False)
+        self._run_check('&#xab &lt;', [('data', '\xab <')], convert_charrefs=True)
+
+        self._run_check('&#123456789 &lt;',
+                        [('charref', '123456789'), ('data', ' '), ('entityref', 'lt')],
+                        convert_charrefs=False)
+        self._run_check('&#123456789 &lt;', [('data', '\ufffd <')],
+                        convert_charrefs=True)
+        self._run_check('&#x123456789 &lt;',
+                        [('charref', 'x123456789'), ('data', ' '), ('entityref', 'lt')],
+                        convert_charrefs=False)
+        self._run_check('&#x123456789 &lt;', [('data', '\ufffd <')],
+                        convert_charrefs=True)
+
+        self._run_check('&# &lt;', [('data', '&# '), ('entityref', 'lt')], convert_charrefs=False)
+        self._run_check('&# &lt;', [('data', '&# <')], convert_charrefs=True)
+        self._run_check('&#x &lt;', [('data', '&#x '), ('entityref', 'lt')], convert_charrefs=False)
+        self._run_check('&#x &lt;', [('data', '&#x <')], convert_charrefs=True)
+
+    def test_eof_in_charref(self):
+        self._run_check('&#123', [('charref', '123')], convert_charrefs=False)
+        self._run_check('&#123', [('data', '{')], convert_charrefs=True)
+        self._run_check('&#xab', [('charref', 'xab')], convert_charrefs=False)
+        self._run_check('&#xab', [('data', '\xab')], convert_charrefs=True)
+
+        self._run_check('&#123456789', [('charref', '123456789')],
+                        convert_charrefs=False)
+        self._run_check('&#123456789', [('data', '\ufffd')], convert_charrefs=True)
+        self._run_check('&#x123456789', [('charref', 'x123456789')],
+                        convert_charrefs=False)
+        self._run_check('&#x123456789', [('data', '\ufffd')], convert_charrefs=True)
+
+        self._run_check('&#', [('data', '&#')], convert_charrefs=False)
+        self._run_check('&#', [('data', '&#')], convert_charrefs=True)
+        self._run_check('&#x', [('data', '&#x')], convert_charrefs=False)
+        self._run_check('&#x', [('data', '&#x')], convert_charrefs=True)
 
     def test_bad_nesting(self):
         # Strangely, this *is* supposed to test that overlapping
@@ -762,20 +840,6 @@ text
         ]
         self._run_check(html, expected)
 
-    def test_EOF_in_charref(self):
-        # see #17802
-        # This test checks that the UnboundLocalError reported in the issue
-        # is not raised, however I'm not sure the returned values are correct.
-        # Maybe HTMLParser should use self.unescape for these
-        data = [
-            ('a&', [('data', 'a&')]),
-            ('a&b', [('data', 'ab')]),
-            ('a&b ', [('data', 'a'), ('entityref', 'b'), ('data', ' ')]),
-            ('a&b;', [('data', 'a'), ('entityref', 'b')]),
-        ]
-        for html, expected in data:
-            self._run_check(html, expected)
-
     def test_eof_in_comments(self):
         data = [
             ('<!--', [('comment', '')]),
diff --git a/Misc/NEWS.d/next/Library/2025-11-02-10-44-23.gh-issue-140875.wt6B37.rst b/Misc/NEWS.d/next/Library/2025-11-02-10-44-23.gh-issue-140875.wt6B37.rst
new file mode 100644
index 00000000000..c08a8966d53
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-11-02-10-44-23.gh-issue-140875.wt6B37.rst
@@ -0,0 +1,3 @@
+Fix handling of unclosed character references (named and numerical)
+followed by the end of file in :class:`html.parser.HTMLParser` with
+``convert_charrefs=False``.