diff --git a/Lib/test/test_htmlparser.py b/Lib/test/test_htmlparser.py
--- a/Lib/test/test_htmlparser.py
+++ b/Lib/test/test_htmlparser.py
@@ -402,6 +402,15 @@
 
         self._run_check(html, expected, collector=self.get_collector())
 
+    def test_with_malformed_attributes(self):
+        # see #12629
+        for html in ['<x><y z=""o"" /></x>', '<x><y z="""" /></x>']:
+            self._run_check(html,
+                            [('starttag', 'x', []),
+                             ('startendtag', 'y', [('z', '')]),
+                             ('endtag', 'x')],
+                            collector=self.get_collector())
+
     def test_comma_between_attributes(self):
         self._run_check('<form action="/xxx.php?a=1&amp;b=2&amp", '
                         'method="post">', [