diff --git a/Lib/cgi.py b/Lib/cgi.py
index 6018c3608697af..6c72507c2087de 100755
--- a/Lib/cgi.py
+++ b/Lib/cgi.py
@@ -115,7 +115,8 @@ def closelog():
 # 0 ==> unlimited input
 maxlen = 0
 
-def parse(fp=None, environ=os.environ, keep_blank_values=0, strict_parsing=0):
+def parse(fp=None, environ=os.environ, keep_blank_values=0,
+          strict_parsing=0, separator='&'):
     """Parse a query in the environment or from a file (default stdin)
 
         Arguments, all optional:
@@ -134,6 +135,9 @@ def parse(fp=None, environ=os.environ, keep_blank_values=0, strict_parsing=0):
         strict_parsing: flag indicating what to do with parsing errors.
             If false (the default), errors are silently ignored.
             If true, errors raise a ValueError exception.
+
+        separator: str. The symbol to use for separating the query arguments.
+            Defaults to &.
     """
     if fp is None:
         fp = sys.stdin
@@ -154,7 +158,7 @@ def parse(fp=None, environ=os.environ, keep_blank_values=0, strict_parsing=0):
     if environ['REQUEST_METHOD'] == 'POST':
         ctype, pdict = parse_header(environ['CONTENT_TYPE'])
         if ctype == 'multipart/form-data':
-            return parse_multipart(fp, pdict)
+            return parse_multipart(fp, pdict, separator=separator)
         elif ctype == 'application/x-www-form-urlencoded':
             clength = int(environ['CONTENT_LENGTH'])
             if maxlen and clength > maxlen:
@@ -178,10 +182,10 @@ def parse(fp=None, environ=os.environ, keep_blank_values=0, strict_parsing=0):
             qs = ""
         environ['QUERY_STRING'] = qs    # XXX Shouldn't, really
     return urllib.parse.parse_qs(qs, keep_blank_values, strict_parsing,
-                                 encoding=encoding)
+                                 encoding=encoding, separator=separator)
 
 
-def parse_multipart(fp, pdict, encoding="utf-8", errors="replace"):
+def parse_multipart(fp, pdict, encoding="utf-8", errors="replace", separator='&'):
     """Parse multipart input.
 
     Arguments:
@@ -205,7 +209,7 @@ def parse_multipart(fp, pdict, encoding="utf-8", errors="replace"):
     except KeyError:
         pass
     fs = FieldStorage(fp, headers=headers, encoding=encoding, errors=errors,
-        environ={'REQUEST_METHOD': 'POST'})
+        environ={'REQUEST_METHOD': 'POST'}, separator=separator)
     return {k: fs.getlist(k) for k in fs}
 
 def _parseparam(s):
@@ -315,7 +319,7 @@ class FieldStorage:
     def __init__(self, fp=None, headers=None, outerboundary=b'',
                  environ=os.environ, keep_blank_values=0, strict_parsing=0,
                  limit=None, encoding='utf-8', errors='replace',
-                 max_num_fields=None):
+                 max_num_fields=None, separator='&'):
         """Constructor.  Read multipart/* until last part.
 
         Arguments, all optional:
@@ -363,6 +367,7 @@ def __init__(self, fp=None, headers=None, outerboundary=b'',
         self.keep_blank_values = keep_blank_values
         self.strict_parsing = strict_parsing
         self.max_num_fields = max_num_fields
+        self.separator = separator
         if 'REQUEST_METHOD' in environ:
             method = environ['REQUEST_METHOD'].upper()
         self.qs_on_post = None
@@ -589,7 +594,7 @@ def read_urlencoded(self):
         query = urllib.parse.parse_qsl(
             qs, self.keep_blank_values, self.strict_parsing,
             encoding=self.encoding, errors=self.errors,
-            max_num_fields=self.max_num_fields)
+            max_num_fields=self.max_num_fields, separator=self.separator)
         self.list = [MiniFieldStorage(key, value) for key, value in query]
         self.skip_lines()
 
@@ -605,7 +610,7 @@ def read_multi(self, environ, keep_blank_values, strict_parsing):
             query = urllib.parse.parse_qsl(
                 self.qs_on_post, self.keep_blank_values, self.strict_parsing,
                 encoding=self.encoding, errors=self.errors,
-                max_num_fields=self.max_num_fields)
+                max_num_fields=self.max_num_fields, separator=self.separator)
             self.list.extend(MiniFieldStorage(key, value) for key, value in query)
 
         klass = self.FieldStorageClass or self.__class__
@@ -649,7 +654,7 @@ def read_multi(self, environ, keep_blank_values, strict_parsing):
                 else self.limit - self.bytes_read
             part = klass(self.fp, headers, ib, environ, keep_blank_values,
                          strict_parsing, limit,
-                         self.encoding, self.errors, max_num_fields)
+                         self.encoding, self.errors, max_num_fields, self.separator)
 
             if max_num_fields is not None:
                 max_num_fields -= 1
diff --git a/Lib/test/test_urlparse.py b/Lib/test/test_urlparse.py
index 28cc3e1ba5fee4..3b1c360625b5a6 100644
--- a/Lib/test/test_urlparse.py
+++ b/Lib/test/test_urlparse.py
@@ -32,6 +32,10 @@
     (b"&a=b", [(b'a', b'b')]),
     (b"a=a+b&b=b+c", [(b'a', b'a b'), (b'b', b'b c')]),
     (b"a=1&a=2", [(b'a', b'1'), (b'a', b'2')]),
+    (";a=b", [(';a', 'b')]),
+    ("a=a+b;b=b+c", [('a', 'a b;b=b c')]),
+    (b";a=b", [(b';a', b'b')]),
+    (b"a=a+b;b=b+c", [(b'a', b'a b;b=b c')]),
 ]
 
 # Each parse_qs testcase is a two-tuple that contains
@@ -58,6 +62,10 @@
     (b"&a=b", {b'a': [b'b']}),
     (b"a=a+b&b=b+c", {b'a': [b'a b'], b'b': [b'b c']}),
     (b"a=1&a=2", {b'a': [b'1', b'2']}),
+    (";a=b", {';a': ['b']}),
+    ("a=a+b;b=b+c", {'a': ['a b;b=b c']}),
+    (b";a=b", {b';a': [b'b']}),
+    (b"a=a+b;b=b+c", {b'a':[ b'a b;b=b c']}),
 ]
 
 class UrlParseTestCase(unittest.TestCase):
@@ -869,7 +877,7 @@ def test_parse_qsl_max_num_fields(self):
         urllib.parse.parse_qs('&'.join(['a=a']*10), max_num_fields=10)
 
     def test_parse_qs_separator(self):
-        semicolon_cases = [
+        parse_qs_semicolon_cases = [
             (";", {}),
             (";;", {}),
             (";a=b", {'a': ['b']}),
@@ -881,13 +889,14 @@ def test_parse_qs_separator(self):
             (b"a=a+b;b=b+c", {b'a': [b'a b'], b'b': [b'b c']}),
             (b"a=1;a=2", {b'a': [b'1', b'2']}),
         ]
-        for orig, expect in semicolon_cases:
-            result = urllib.parse.parse_qs(orig, separator=';')
-            self.assertEqual(result, expect, "Error parsing %r" % orig)
+        for orig, expect in parse_qs_semicolon_cases:
+            with self.subTest(f"Original: {orig!r}, Expected: {expect!r}"):
+                result = urllib.parse.parse_qs(orig, separator=';')
+                self.assertEqual(result, expect, "Error parsing %r" % orig)
 
 
     def test_parse_qsl_separator(self):
-        semicolon_cases = [
+        parse_qsl_semicolon_cases = [
             (";", []),
             (";;", []),
             (";a=b", [('a', 'b')]),
@@ -899,9 +908,11 @@ def test_parse_qsl_separator(self):
             (b"a=a+b;b=b+c", [(b'a', b'a b'), (b'b', b'b c')]),
             (b"a=1;a=2", [(b'a', b'1'), (b'a', b'2')]),
         ]
-        for orig, expect in semicolon_cases:
-            result = urllib.parse.parse_qsl(orig, separator=';')
-            self.assertEqual(result, expect, "Error parsing %r" % orig)
+        for orig, expect in parse_qsl_semicolon_cases:
+            with self.subTest(f"Original: {orig!r}, Expected: {expect!r}"):
+                result = urllib.parse.parse_qsl(orig, separator=';')
+                self.assertEqual(result, expect, "Error parsing %r" % orig)
+
 
     def test_urlencode_sequences(self):
         # Other tests incidentally urlencode things; test non-covered cases:
diff --git a/Lib/urllib/parse.py b/Lib/urllib/parse.py
index e07db8368616f2..5bd067895bfa3d 100644
--- a/Lib/urllib/parse.py
+++ b/Lib/urllib/parse.py
@@ -734,6 +734,10 @@ def parse_qsl(qs, keep_blank_values=False, strict_parsing=False,
     """
     qs, _coerce_result = _coerce_args(qs)
 
+    if not separator or (not isinstance(separator, str)
+        and not isinstance(separator, bytes)):
+        raise ValueError("Separator must be of type string or bytes.")
+
     # If max_num_fields is defined then check that the number of fields
     # is less than max_num_fields. This prevents a memory exhaustion DOS
     # attack via post bodies with many fields.