diff --git a/Lib/_markupbase.py b/Lib/_markupbase.py
index 98b9037afff..2af5f1c23b6 100644
--- a/Lib/_markupbase.py
+++ b/Lib/_markupbase.py
@@ -107,6 +107,10 @@ class ParserBase:
                 if decltype == "doctype":
                     self.handle_decl(data)
                 else:
+                    # According to the HTML5 specs sections "8.2.4.44 Bogus
+                    # comment state" and "8.2.4.45 Markup declaration open
+                    # state", a comment token should be emitted.
+                    # Calling unknown_decl provides more flexibility though.
                     self.unknown_decl(data)
                 return j + 1
             if c in "\"'":
diff --git a/Lib/test/test_htmlparser.py b/Lib/test/test_htmlparser.py
index 87b5060611d..8c2e25e61a6 100644
--- a/Lib/test/test_htmlparser.py
+++ b/Lib/test/test_htmlparser.py
@@ -323,6 +323,16 @@ DOCTYPE html [
                                 ("endtag", element_lower)],
                             collector=Collector())
 
+    def test_condcoms(self):
+        html = ('<!--[if IE & !(lte IE 8)]>aren\'t<![endif]-->'
+                '<!--[if IE 8]>condcoms<![endif]-->'
+                '<!--[if lte IE 7]>pretty?<![endif]-->')
+        expected = [('comment', "[if IE & !(lte IE 8)]>aren't<![endif]"),
+                    ('comment', '[if IE 8]>condcoms<![endif]'),
+                    ('comment', '[if lte IE 7]>pretty?<![endif]')]
+        self._run_check(html, expected)
+
+
 class HTMLParserTolerantTestCase(HTMLParserStrictTestCase):
 
     def get_collector(self):
@@ -416,6 +426,39 @@ class HTMLParserTolerantTestCase(HTMLParserStrictTestCase):
         # see #12888
         self.assertEqual(p.unescape('&#123; ' * 1050), '{ ' * 1050)
 
+    def test_broken_condcoms(self):
+        # these condcoms are missing the '--' after '<!' and before the '>'
+        html = ('<![if !(IE)]>broken condcom<![endif]>'
+                '<![if ! IE]><link href="favicon.tiff"/><![endif]>'
+                '<![if !IE 6]><img src="firefox.png" /><![endif]>'
+                '<![if !ie 6]><b>foo</b><![endif]>'
+                '<![if (!IE)|(lt IE 9)]><img src="mammoth.bmp" /><![endif]>')
+        # According to the HTML5 specs sections "8.2.4.44 Bogus comment state"
+        # and "8.2.4.45 Markup declaration open state", comment tokens should
+        # be emitted instead of 'unknown decl', but calling unknown_decl
+        # provides more flexibility.
+        # See also Lib/_markupbase.py:parse_declaration
+        expected = [
+            ('unknown decl', 'if !(IE)'),
+            ('data', 'broken condcom'),
+            ('unknown decl', 'endif'),
+            ('unknown decl', 'if ! IE'),
+            ('startendtag', 'link', [('href', 'favicon.tiff')]),
+            ('unknown decl', 'endif'),
+            ('unknown decl', 'if !IE 6'),
+            ('startendtag', 'img', [('src', 'firefox.png')]),
+            ('unknown decl', 'endif'),
+            ('unknown decl', 'if !ie 6'),
+            ('starttag', 'b', []),
+            ('data', 'foo'),
+            ('endtag', 'b'),
+            ('unknown decl', 'endif'),
+            ('unknown decl', 'if (!IE)|(lt IE 9)'),
+            ('startendtag', 'img', [('src', 'mammoth.bmp')]),
+            ('unknown decl', 'endif')
+        ]
+        self._run_check(html, expected)
+
 
 class AttributesStrictTestCase(TestCaseBase):