diff --git a/Lib/html/parser.py b/Lib/html/parser.py
index afdb305d08c..662e85575a4 100644
--- a/Lib/html/parser.py
+++ b/Lib/html/parser.py
@@ -30,8 +30,8 @@ attrfind = re.compile(
     r'\s*([a-zA-Z_][-.:a-zA-Z_0-9]*)(\s*=\s*'
     r'(\'[^\']*\'|"[^"]*"|[^\s"\'=<>`]*))?')
 attrfind_tolerant = re.compile(
-    r',?\s*([a-zA-Z_][-.:a-zA-Z_0-9]*)(\s*=\s*'
-    r'(\'[^\']*\'|"[^"]*"|[^>\s]*))?')
+    r'\s*((?<=[\'"\s])[^\s/>][^\s/=>]*)(\s*=+\s*'
+    r'(\'[^\']*\'|"[^"]*"|(?![\'"])[^>\s]*))?')
 locatestarttagend = re.compile(r"""
   <[a-zA-Z][-.a-zA-Z0-9:_]*          # tag name
   (?:\s+                             # whitespace before attribute name
@@ -49,16 +49,16 @@ locatestarttagend = re.compile(r"""
 locatestarttagend_tolerant = re.compile(r"""
   <[a-zA-Z][-.a-zA-Z0-9:_]*          # tag name
   (?:\s*                             # optional whitespace before attribute name
-    (?:[a-zA-Z_][-.:a-zA-Z0-9_]*     # attribute name
-      (?:\s*=\s*                     # value indicator
+    (?:(?<=['"\s])[^\s/>][^\s/=>]*   # attribute name
+      (?:\s*=+\s*                    # value indicator
         (?:'[^']*'                   # LITA-enclosed value
-          |\"[^\"]*\"                # LIT-enclosed value
-          |[^'\">\s]+                # bare value
+          |"[^"]*"                   # LIT-enclosed value
+          |(?!['"])[^>\s]*           # bare value
          )
          (?:\s*,)*                   # possibly followed by a comma
-       )?
-     )
-   )*
+       )?\s*
+     )*
+   )?
   \s*                                # trailing whitespace
 """, re.VERBOSE)
 endendtag = re.compile('>')
@@ -295,6 +295,7 @@ class HTMLParser(_markupbase.ParserBase):
             elif attrvalue[:1] == '\'' == attrvalue[-1:] or \
                  attrvalue[:1] == '"' == attrvalue[-1:]:
                 attrvalue = attrvalue[1:-1]
+            if attrvalue:
                 attrvalue = self.unescape(attrvalue)
             attrs.append((attrname.lower(), attrvalue))
             k = m.end()
diff --git a/Lib/test/test_htmlparser.py b/Lib/test/test_htmlparser.py
index b587ab80d54..1ce4594a44a 100644
--- a/Lib/test/test_htmlparser.py
+++ b/Lib/test/test_htmlparser.py
@@ -196,60 +196,6 @@ DOCTYPE html [
             ("data", "this < text > contains < bare>pointy< brackets"),
             ])
 
-    def test_attr_syntax(self):
-        output = [
-          ("starttag", "a", [("b", "v"), ("c", "v"), ("d", "v"), ("e", None)])
-          ]
-        self._run_check("""<a b='v' c="v" d=v e>""", output)
-        self._run_check("""<a  b = 'v' c = "v" d = v e>""", output)
-        self._run_check("""<a\nb\n=\n'v'\nc\n=\n"v"\nd\n=\nv\ne>""", output)
-        self._run_check("""<a\tb\t=\t'v'\tc\t=\t"v"\td\t=\tv\te>""", output)
-
-    def test_attr_values(self):
-        self._run_check("""<a b='xxx\n\txxx' c="yyy\t\nyyy" d='\txyz\n'>""",
-                        [("starttag", "a", [("b", "xxx\n\txxx"),
-                                            ("c", "yyy\t\nyyy"),
-                                            ("d", "\txyz\n")])
-                         ])
-        self._run_check("""<a b='' c="">""", [
-            ("starttag", "a", [("b", ""), ("c", "")]),
-            ])
-        # Regression test for SF patch #669683.
-        self._run_check("<e a=rgb(1,2,3)>", [
-            ("starttag", "e", [("a", "rgb(1,2,3)")]),
-            ])
-        # Regression test for SF bug #921657.
-        self._run_check("<a href=mailto:xyz@example.com>", [
-            ("starttag", "a", [("href", "mailto:xyz@example.com")]),
-            ])
-
-    def test_attr_nonascii(self):
-        # see issue 7311
-        self._run_check("<img src=/foo/bar.png alt=\u4e2d\u6587>", [
-            ("starttag", "img", [("src", "/foo/bar.png"),
-                                 ("alt", "\u4e2d\u6587")]),
-            ])
-        self._run_check("<a title='\u30c6\u30b9\u30c8' "
-                        "href='\u30c6\u30b9\u30c8.html'>", [
-            ("starttag", "a", [("title", "\u30c6\u30b9\u30c8"),
-                               ("href", "\u30c6\u30b9\u30c8.html")]),
-            ])
-        self._run_check('<a title="\u30c6\u30b9\u30c8" '
-                        'href="\u30c6\u30b9\u30c8.html">', [
-            ("starttag", "a", [("title", "\u30c6\u30b9\u30c8"),
-                               ("href", "\u30c6\u30b9\u30c8.html")]),
-            ])
-
-    def test_attr_entity_replacement(self):
-        self._run_check("""<a b='&amp;&gt;&lt;&quot;&apos;'>""", [
-            ("starttag", "a", [("b", "&><\"'")]),
-            ])
-
-    def test_attr_funky_names(self):
-        self._run_check("""<a a.b='v' c:d=v e-f=v>""", [
-            ("starttag", "a", [("a.b", "v"), ("c:d", "v"), ("e-f", "v")]),
-            ])
-
     def test_illegal_declarations(self):
         self._parse_error('<!spacer type="block" height="25">')
 
@@ -295,13 +241,11 @@ DOCTYPE html [
         self._parse_error("<a<a>")
         self._parse_error("</a<a>")
         self._parse_error("<!")
-        self._parse_error("<a $>")
         self._parse_error("<a")
         self._parse_error("<a foo='bar'")
         self._parse_error("<a foo='bar")
         self._parse_error("<a foo='>'")
         self._parse_error("<a foo='>")
-        self._parse_error("<a foo=>")
 
     def test_declaration_junk_chars(self):
         self._parse_error("<!DOCTYPE foo $ >")
@@ -358,10 +302,6 @@ DOCTYPE html [
                                     ("endtag", element_lower)])
 
 
-    def test_entityrefs_in_attributes(self):
-        self._run_check("<html foo='&euro;&amp;&#97;&#x61;&unsupported;'>",
-                        [("starttag", "html", [("foo", "\u20AC&aa&unsupported;")])])
-
 
 class HTMLParserTolerantTestCase(HTMLParserStrictTestCase):
 
@@ -371,15 +311,14 @@ class HTMLParserTolerantTestCase(HTMLParserStrictTestCase):
     def test_tolerant_parsing(self):
         self._run_check('<html <html>te>>xt&a<<bc</a></html>\n'
                         '<img src="URL><//img></html</html>', [
-                             ('data', '<html '),
-                             ('starttag', 'html', []),
-                             ('data', 'te>>xt'),
-                             ('entityref', 'a'),
-                             ('data', '<<bc'),
-                             ('endtag', 'a'),
-                             ('endtag', 'html'),
-                             ('data', '\n<img src="URL><//img></html'),
-                             ('endtag', 'html')])
+                            ('starttag', 'html', [('<html', None)]),
+                            ('data', 'te>>xt'),
+                            ('entityref', 'a'),
+                            ('data', '<<bc'),
+                            ('endtag', 'a'),
+                            ('endtag', 'html'),
+                            ('data', '\n<img src="URL><//img></html'),
+                            ('endtag', 'html')])
 
     def test_with_unquoted_attributes(self):
         # see #12008
@@ -410,7 +349,7 @@ class HTMLParserTolerantTestCase(HTMLParserStrictTestCase):
                         'method="post">', [
                             ('starttag', 'form',
                                 [('action', '/xxx.php?a=1&b=2&amp'),
-                                 ('method', 'post')])])
+                                 (',', None), ('method', 'post')])])
 
     def test_weird_chars_in_unquoted_attribute_values(self):
         self._run_check('<form action=bogus|&#()value>', [
@@ -441,7 +380,7 @@ class HTMLParserTolerantTestCase(HTMLParserStrictTestCase):
 
         html = '<div style="", foo = "bar" ><b>The <a href="some_url">rain</a>'
         expected = [
-            ('starttag', 'div', [('style', ''), ('foo', 'bar')]),
+            ('starttag', 'div', [('style', ''), (',', None), ('foo', 'bar')]),
             ('starttag', 'b', []),
             ('data', 'The '),
             ('starttag', 'a', [('href', 'some_url')]),
@@ -458,8 +397,151 @@ class HTMLParserTolerantTestCase(HTMLParserStrictTestCase):
         self.assertEqual(p.unescape('&#123; ' * 1050), '{ ' * 1050)
 
 
+class AttributesStrictTestCase(TestCaseBase):
+
+    def get_collector(self):
+        return EventCollector(strict=True)
+
+    def test_attr_syntax(self):
+        output = [
+          ("starttag", "a", [("b", "v"), ("c", "v"), ("d", "v"), ("e", None)])
+        ]
+        self._run_check("""<a b='v' c="v" d=v e>""", output)
+        self._run_check("""<a  b = 'v' c = "v" d = v e>""", output)
+        self._run_check("""<a\nb\n=\n'v'\nc\n=\n"v"\nd\n=\nv\ne>""", output)
+        self._run_check("""<a\tb\t=\t'v'\tc\t=\t"v"\td\t=\tv\te>""", output)
+
+    def test_attr_values(self):
+        self._run_check("""<a b='xxx\n\txxx' c="yyy\t\nyyy" d='\txyz\n'>""",
+                        [("starttag", "a", [("b", "xxx\n\txxx"),
+                                            ("c", "yyy\t\nyyy"),
+                                            ("d", "\txyz\n")])])
+        self._run_check("""<a b='' c="">""",
+                        [("starttag", "a", [("b", ""), ("c", "")])])
+        # Regression test for SF patch #669683.
+        self._run_check("<e a=rgb(1,2,3)>",
+                        [("starttag", "e", [("a", "rgb(1,2,3)")])])
+        # Regression test for SF bug #921657.
+        self._run_check(
+            "<a href=mailto:xyz@example.com>",
+            [("starttag", "a", [("href", "mailto:xyz@example.com")])])
+
+    def test_attr_nonascii(self):
+        # see issue 7311
+        self._run_check(
+            "<img src=/foo/bar.png alt=\u4e2d\u6587>",
+            [("starttag", "img", [("src", "/foo/bar.png"),
+                                  ("alt", "\u4e2d\u6587")])])
+        self._run_check(
+            "<a title='\u30c6\u30b9\u30c8' href='\u30c6\u30b9\u30c8.html'>",
+            [("starttag", "a", [("title", "\u30c6\u30b9\u30c8"),
+                                ("href", "\u30c6\u30b9\u30c8.html")])])
+        self._run_check(
+            '<a title="\u30c6\u30b9\u30c8" href="\u30c6\u30b9\u30c8.html">',
+            [("starttag", "a", [("title", "\u30c6\u30b9\u30c8"),
+                                ("href", "\u30c6\u30b9\u30c8.html")])])
+
+    def test_attr_entity_replacement(self):
+        self._run_check(
+            "<a b='&amp;&gt;&lt;&quot;&apos;'>",
+            [("starttag", "a", [("b", "&><\"'")])])
+
+    def test_attr_funky_names(self):
+        self._run_check(
+            "<a a.b='v' c:d=v e-f=v>",
+            [("starttag", "a", [("a.b", "v"), ("c:d", "v"), ("e-f", "v")])])
+
+    def test_entityrefs_in_attributes(self):
+        self._run_check(
+            "<html foo='&euro;&amp;&#97;&#x61;&unsupported;'>",
+            [("starttag", "html", [("foo", "\u20AC&aa&unsupported;")])])
+
+
+
+class AttributesTolerantTestCase(AttributesStrictTestCase):
+
+    def get_collector(self):
+        return EventCollector(strict=False)
+
+    def test_attr_funky_names2(self):
+        self._run_check(
+            "<a $><b $=%><c \=/>",
+            [("starttag", "a", [("$", None)]),
+             ("starttag", "b", [("$", "%")]),
+             ("starttag", "c", [("\\", "/")])])
+
+    def test_entities_in_attribute_value(self):
+        # see #1200313
+        for entity in ['&', '&amp;', '&#38;', '&#x26;']:
+            self._run_check('<a href="%s">' % entity,
+                            [("starttag", "a", [("href", "&")])])
+            self._run_check("<a href='%s'>" % entity,
+                            [("starttag", "a", [("href", "&")])])
+            self._run_check("<a href=%s>" % entity,
+                            [("starttag", "a", [("href", "&")])])
+
+    def test_malformed_attributes(self):
+        # see #13357
+        html = (
+            "<a href=test'style='color:red;bad1'>test - bad1</a>"
+            "<a href=test'+style='color:red;ba2'>test - bad2</a>"
+            "<a href=test'&nbsp;style='color:red;bad3'>test - bad3</a>"
+            "<a href = test'&nbsp;style='color:red;bad4'  >test - bad4</a>"
+        )
+        expected = [
+            ('starttag', 'a', [('href', "test'style='color:red;bad1'")]),
+            ('data', 'test - bad1'), ('endtag', 'a'),
+            ('starttag', 'a', [('href', "test'+style='color:red;ba2'")]),
+            ('data', 'test - bad2'), ('endtag', 'a'),
+            ('starttag', 'a', [('href', "test'\xa0style='color:red;bad3'")]),
+            ('data', 'test - bad3'), ('endtag', 'a'),
+            ('starttag', 'a', [('href', "test'\xa0style='color:red;bad4'")]),
+            ('data', 'test - bad4'), ('endtag', 'a')
+        ]
+        self._run_check(html, expected)
+
+    def test_malformed_adjacent_attributes(self):
+        # see #12629
+        self._run_check('<x><y z=""o"" /></x>',
+                        [('starttag', 'x', []),
+                            ('startendtag', 'y', [('z', ''), ('o""', None)]),
+                            ('endtag', 'x')])
+        self._run_check('<x><y z="""" /></x>',
+                        [('starttag', 'x', []),
+                            ('startendtag', 'y', [('z', ''), ('""', None)]),
+                            ('endtag', 'x')])
+
+    # see #755670 for the following 3 tests
+    def test_adjacent_attributes(self):
+        self._run_check('<a width="100%"cellspacing=0>',
+                        [("starttag", "a",
+                          [("width", "100%"), ("cellspacing","0")])])
+
+        self._run_check('<a id="foo"class="bar">',
+                        [("starttag", "a",
+                          [("id", "foo"), ("class","bar")])])
+
+    def test_missing_attribute_value(self):
+        self._run_check('<a v=>',
+                        [("starttag", "a", [("v", "")])])
+
+    def test_javascript_attribute_value(self):
+        self._run_check("<a href=javascript:popup('/popup/help.html')>",
+                        [("starttag", "a",
+                          [("href", "javascript:popup('/popup/help.html')")])])
+
+    def test_end_tag_in_attribute_value(self):
+        # see #1745761
+        self._run_check("<a href='http://www.example.org/\">;'>spam</a>",
+                        [("starttag", "a",
+                          [("href", "http://www.example.org/\">;")]),
+                         ("data", "spam"), ("endtag", "a")])
+
+
+
 def test_main():
-    support.run_unittest(HTMLParserStrictTestCase, HTMLParserTolerantTestCase)
+    support.run_unittest(HTMLParserStrictTestCase, HTMLParserTolerantTestCase,
+                         AttributesStrictTestCase, AttributesTolerantTestCase)
 
 
 if __name__ == "__main__":
diff --git a/Misc/NEWS b/Misc/NEWS
index 05ff988c2e1..c462d6fe2d7 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -365,6 +365,9 @@ Core and Builtins
 Library
 -------
 
+- Issues #1745761, #755670, #13357, #12629, #1200313: HTMLParser now correctly
+  handles non-valid attributes, including adjacent and unquoted attributes.
+
 - Issue #13193: Fix distutils.filelist.FileList and
   packaging.manifest.Manifest under Windows.  The "recursive-include"
   directive now recognizes both legal path separators.