diff --git a/bleach/sanitizer.py b/bleach/sanitizer.py
index c60c26b..79b80f5 100644
--- a/bleach/sanitizer.py
+++ b/bleach/sanitizer.py
@@ -395,7 +395,18 @@ class BleachSanitizerFilter(html5lib_shim.SanitizerFilter):
             if part.startswith('&'):
                 entity = html5lib_shim.match_entity(part)
                 if entity is not None:
-                    new_tokens.append({'type': 'Entity', 'name': entity})
+                    if entity == 'amp':
+                        # LinkifyFilter can't match urls across token boundaries
+                        # which is problematic with &amp; since that shows up in
+                        # querystrings all the time. This special-cases &amp;
+                        # and converts it to a & and sticks it in as a
+                        # Characters token. It'll get merged with surrounding
+                        # tokens in the BleachSanitizerfilter.__iter__ and
+                        # escaped in the serializer.
+                        new_tokens.append({'type': 'Characters', 'data': '&'})
+                    else:
+                        new_tokens.append({'type': 'Entity', 'name': entity})
+
                     # Length of the entity plus 2--one for & at the beginning
                     # and and one for ; at the end
                     remainder = part[len(entity) + 2:]

diff --git a/tests/test_linkify.py b/tests/test_linkify.py
index 584a5b0..ab1c513 100644
--- a/tests/test_linkify.py
+++ b/tests/test_linkify.py
@@ -694,6 +694,10 @@ class TestLinkify:
         'http://example.com?b=1&c=2',
         '<a href="http://example.com?b=1&amp;c=2">http://example.com?b=1&amp;c=2</a>'
     ),
+    (
+        'http://example.com?b=1&amp;c=2',
+        '<a href="http://example.com?b=1&amp;c=2">http://example.com?b=1&amp;c=2</a>'
+    ),
     (
         'link: https://example.com/watch#anchor',
         'link: <a href="https://example.com/watch#anchor">https://example.com/watch#anchor</a>'

LinkifyFilter with clean breaks links at &amp;
(Split out to a new issue from [this comment](https://github.com/mozilla/bleach/issues/419#issuecomment-445056894))

When using `LinkifyFilter` instead of the stand-alone `linkify`, links are broken at any `&amp;`, but not bare `&` characters.

Here's a pretty minimal demonstration:

```
import bleach

bleach.linkify("https://www.youtube.com/watch?v=SkcucKDrbOI&amp;feature=youtu.be")
```

Result (expected): `<a href="https://www.youtube.com/watch?v=SkcucKDrbOI&amp;feature=youtu.be" rel="nofollow">https://www.youtube.com/watch?v=SkcucKDrbOI&amp;feature=youtu.be</a>`

```
import bleach
from functools import partial

bleach_linkifier = partial(bleach.linkifier.LinkifyFilter)
cleaner = bleach.Cleaner(filters=[bleach_linkifier])
cleaner.clean("https://www.youtube.com/watch?v=SkcucKDrbOI&amp;feature=youtu.be")
```

Result (not expected, link stops at the `&amp;`): `<a href="https://www.youtube.com/watch?v=SkcucKDrbOI">https://www.youtube.com/watch?v=SkcucKDrbOI</a>&amp;feature=<a href="http://youtu.be">youtu.be</a>`

It works with just a bare `&` instead of the `&amp;`, like `https://www.youtube.com/watch?v=SkcucKDrbOI&feature=youtu.be`. In that case, the output of both methods is:

```
<a href="https://www.youtube.com/watch?v=SkcucKDrbOI&amp;feature=youtu.be">https://www.youtube.com/watch?v=SkcucKDrbOI&amp;feature=youtu.be</a>
```

(with an additional `rel="nofollow"` attr added by `linkify()` by default)
tests/test_linkify.py::test_linkify_filter[http://example.com?b=1&amp;c=2-<a
tests/test_linkify.py::test_empty tests/test_linkify.py::test_simple_link tests/test_linkify.py::test_trailing_slash tests/test_linkify.py::test_mangle_link tests/test_linkify.py::test_mangle_text tests/test_linkify.py::test_invalid_attribute_names tests/test_linkify.py::test_email_link[a tests/test_linkify.py::test_email_link[aussie tests/test_linkify.py::test_email_link[email tests/test_linkify.py::test_email_link[<br>jinkyun@example.com-True-<br><a tests/test_linkify.py::test_email_link[mailto tests/test_linkify.py::test_email_link["\\\n"@opa.ru-True-"\\\n"@opa.ru] tests/test_linkify.py::test_email_link_escaping["james"@example.com-<a tests/test_linkify.py::test_email_link_escaping["j'ames"@example.com-<a tests/test_linkify.py::test_email_link_escaping["ja>mes"@example.com-<a tests/test_linkify.py::test_prevent_links[callback0-a tests/test_linkify.py::test_prevent_links[callback1-a tests/test_linkify.py::test_prevent_links[callback2-a tests/test_linkify.py::test_prevent_links[callback3-a tests/test_linkify.py::test_prevent_links[callback4-a tests/test_linkify.py::test_prevent_links[callback5-a tests/test_linkify.py::test_set_attrs tests/test_linkify.py::test_only_proto_links tests/test_linkify.py::test_stop_email tests/test_linkify.py::test_tlds[example.com-<a tests/test_linkify.py::test_tlds[example.co-<a tests/test_linkify.py::test_tlds[example.co.uk-<a tests/test_linkify.py::test_tlds[example.edu-<a tests/test_linkify.py::test_tlds[example.xxx-<a tests/test_linkify.py::test_tlds[bit.ly/fun-<a tests/test_linkify.py::test_tlds[example.yyy-example.yyy] tests/test_linkify.py::test_tlds[brie-brie] tests/test_linkify.py::test_escaping tests/test_linkify.py::test_nofollow_off tests/test_linkify.py::test_link_in_html tests/test_linkify.py::test_links_https tests/test_linkify.py::test_add_rel_nofollow tests/test_linkify.py::test_url_with_path tests/test_linkify.py::test_link_ftp tests/test_linkify.py::test_link_query tests/test_linkify.py::test_link_fragment tests/test_linkify.py::test_link_entities tests/test_linkify.py::test_escaped_html tests/test_linkify.py::test_link_http_complete tests/test_linkify.py::test_non_url tests/test_linkify.py::test_javascript_url tests/test_linkify.py::test_unsafe_url tests/test_linkify.py::test_skip_tags tests/test_linkify.py::test_libgl tests/test_linkify.py::test_end_of_sentence[example.com-.] tests/test_linkify.py::test_end_of_sentence[example.com-...] tests/test_linkify.py::test_end_of_sentence[ex.com/foo-.] tests/test_linkify.py::test_end_of_sentence[ex.com/foo-....] tests/test_linkify.py::test_end_of_clause tests/test_linkify.py::test_sarcasm tests/test_linkify.py::test_wrapping_parentheses[(example.com)-expected_data0] tests/test_linkify.py::test_wrapping_parentheses[(example.com/)-expected_data1] tests/test_linkify.py::test_wrapping_parentheses[(example.com/foo)-expected_data2] tests/test_linkify.py::test_wrapping_parentheses[(((example.com/))))-expected_data3] tests/test_linkify.py::test_wrapping_parentheses[example.com/))-expected_data4] tests/test_linkify.py::test_wrapping_parentheses[(foo tests/test_linkify.py::test_wrapping_parentheses[http://en.wikipedia.org/wiki/Test_(assessment)-expected_data7] tests/test_linkify.py::test_wrapping_parentheses[(http://en.wikipedia.org/wiki/Test_(assessment))-expected_data8] tests/test_linkify.py::test_wrapping_parentheses[((http://en.wikipedia.org/wiki/Test_(assessment))-expected_data9] tests/test_linkify.py::test_wrapping_parentheses[(http://en.wikipedia.org/wiki/Test_(assessment)))-expected_data10] tests/test_linkify.py::test_wrapping_parentheses[(http://en.wikipedia.org/wiki/)Test_(assessment-expected_data11] tests/test_linkify.py::test_wrapping_parentheses[hello tests/test_linkify.py::test_parentheses_with_removing tests/test_linkify.py::test_ports[http://foo.com:8000-expected_data0] tests/test_linkify.py::test_ports[http://foo.com:8000/-expected_data1] tests/test_linkify.py::test_ports[http://bar.com:xkcd-expected_data2] tests/test_linkify.py::test_ports[http://foo.com:81/bar-expected_data3] tests/test_linkify.py::test_ports[http://foo.com:-expected_data4] tests/test_linkify.py::test_ports[http://foo.com:\u0663\u0669/-expected_data5] tests/test_linkify.py::test_ports[http://foo.com:\U0001d7e0\U0001d7d8/-expected_data6] tests/test_linkify.py::test_ignore_bad_protocols tests/test_linkify.py::test_link_emails_and_urls tests/test_linkify.py::test_links_case_insensitive tests/test_linkify.py::test_elements_inside_links tests/test_linkify.py::test_drop_link_tags tests/test_linkify.py::test_naughty_unescaping[&lt;br&gt;-&lt;br&gt;] tests/test_linkify.py::test_naughty_unescaping[&lt;br&gt; tests/test_linkify.py::test_hang tests/test_linkify.py::test_hyphen_in_mail tests/test_linkify.py::test_url_re_arg tests/test_linkify.py::test_email_re_arg tests/test_linkify.py::test_recognized_tags_arg tests/test_linkify.py::test_linkify_idempotent tests/test_linkify.py::TestLinkify::test_no_href_links tests/test_linkify.py::TestLinkify::test_rel_already_there tests/test_linkify.py::TestLinkify::test_only_text_is_linkified tests/test_linkify.py::test_linkify_filter[abc-abc] tests/test_linkify.py::test_linkify_filter[example.com-<a tests/test_linkify.py::test_linkify_filter[http://example.com?b=1&c=2-<a tests/test_linkify.py::test_linkify_filter[link: