diff --git a/dulwich/objects.py b/dulwich/objects.py
index 74ade5c1e..92456a584 100644
--- a/dulwich/objects.py
+++ b/dulwich/objects.py
@@ -27,6 +27,7 @@
 import os
 import posixpath
 import stat
+import re
 from typing import (
     Optional,
     Dict,
@@ -70,6 +71,11 @@
 
 S_IFGITLINK = 0o160000
 
+# Intentionally flexible to support various types of brokenness
+_TIME_ENTRY_RE = re.compile(
+    b"^(?P<person>.*) (?P<time>-?[0-9]+) (?P<timezone>[+-]{0,2}[0-9]+)$"
+)
+
 
 MAX_TIME = 9223372036854775807  # (2**63) - 1 - signed long int max
 
@@ -1211,11 +1217,13 @@ def parse_timezone(text):
         and a boolean indicating whether this was a UTC timezone
         prefixed with a negative sign (-0000).
     """
+    if text[0] not in b"+-":
+        # Some (broken) commits do not have a sign
+        text = b"+" + text
+
     # cgit parses the first character as the sign, and the rest
     #  as an integer (using strtol), which could also be negative.
     #  We do the same for compatibility. See #697828.
-    if not text[0] in b"+-":
-        raise ValueError("Timezone must start with + or - (%(text)s)" % vars())
     sign = text[:1]
     offset = int(text[1:])
     if sign == b"-":
@@ -1259,18 +1267,16 @@ def parse_time_entry(value):
       field date)
     Returns: Tuple of (author, time, (timezone, timezone_neg_utc))
     """
-    try:
-        sep = value.rindex(b"> ")
-    except ValueError:
-        return (value, None, (None, False))
-    try:
-        person = value[0 : sep + 1]
-        rest = value[sep + 2 :]
-        timetext, timezonetext = rest.rsplit(b" ", 1)
-        time = int(timetext)
-        timezone, timezone_neg_utc = parse_timezone(timezonetext)
-    except ValueError as e:
-        raise ObjectFormatException(e)
+    m = _TIME_ENTRY_RE.match(value)
+    if not m:
+        raise ObjectFormatException("foo")
+
+    person = m.group("person")
+    timetext = m.group("time")
+    timezonetext = m.group("timezone")
+    time = int(timetext)
+    timezone, timezone_neg_utc = parse_timezone(timezonetext)
+
     return person, time, (timezone, timezone_neg_utc)
 
 
diff --git a/dulwich/tests/test_objects.py b/dulwich/tests/test_objects.py
index d2c37455b..bf71afd78 100644
--- a/dulwich/tests/test_objects.py
+++ b/dulwich/tests/test_objects.py
@@ -712,6 +712,103 @@ def test_check_commit_with_overflow_date(self):
             with self.assertRaises(ObjectFormatException):
                 commit.check()
 
+    def test_check_commit_with_negative_date(self):
+        author_line = (
+            b'Jane Doe <jdoe@example.org> -12345 +0100'
+        )
+        expected_identity = b'Jane Doe <jdoe@example.org>'
+        expected_time = -12345
+        expected_timezone = +1 * 60 * 60
+        commit = Commit.from_string(self.make_commit_text(author=author_line))
+
+        # The commit parses properly
+        self.assertEqual(commit.author, expected_identity)
+        self.assertEqual(commit.author_time, expected_time)
+        self.assertEqual(commit.author_timezone, expected_timezone)
+
+        commit.check()
+
+    def test_check_commit_with_double_negative_timezone(self):
+        author_line = (
+            b'Jane Doe <jdoe@example.org> 12345 --700'
+        )
+        expected_identity = b'Jane Doe <jdoe@example.org>'
+        expected_time = 12345
+        expected_timezone = +7 * 60 * 60
+        commit = Commit.from_string(self.make_commit_text(author=author_line))
+
+        # The commit parses properly
+        self.assertEqual(commit.author, expected_identity)
+        self.assertEqual(commit.author_time, expected_time)
+        self.assertEqual(commit.author_timezone, expected_timezone)
+
+        commit.check()
+
+    def test_commit_with_long_timezone(self):
+        author_line = (
+            b'Geoff Cant <nem@lisp.geek.nz> 1170648114 -72000'
+        )
+        expected_identity = b'Geoff Cant <nem@lisp.geek.nz>'
+        expected_time = 1170648114
+        expected_timezone = -720 * 60 * 60
+        commit = Commit.from_string(self.make_commit_text(author=author_line))
+
+        # The commit parses properly
+        self.assertEqual(commit.author, expected_identity)
+        self.assertEqual(commit.author_time, expected_time)
+        self.assertEqual(commit.author_timezone, expected_timezone)
+
+        commit.check()
+
+    def test_commit_with_short_timezone(self):
+        author_line = (
+            b'Pl\xc3\xa1cidoMonteiro <Pl\xc3\xa1cidoMonteiro@.(none)> 1380083482 +02'
+        )
+        expected_identity = b'Pl\xc3\xa1cidoMonteiro <Pl\xc3\xa1cidoMonteiro@.(none)>'
+        expected_time = 1380083482
+        expected_timezone = +2 * 60
+        commit = Commit.from_string(self.make_commit_text(author=author_line))
+
+        # The commit parses properly
+        self.assertEqual(commit.author, expected_identity)
+        self.assertEqual(commit.author_time, expected_time)
+        self.assertEqual(commit.author_timezone, expected_timezone)
+
+        commit.check()
+
+    def test_commit_with_unsigned_timezone(self):
+        author_line = (
+            b'applehq <applehq@203d044e-caa7-11dc-91ec-67e1038599e7> 1205785941 0000'
+        )
+        expected_identity = b'applehq <applehq@203d044e-caa7-11dc-91ec-67e1038599e7>'
+        expected_time = 1205785941
+        expected_timezone = 0
+        commit = Commit.from_string(self.make_commit_text(author=author_line))
+
+        # The commit parses properly
+        self.assertEqual(commit.author, expected_identity)
+        self.assertEqual(commit.author_time, expected_time)
+        self.assertEqual(commit.author_timezone, expected_timezone)
+
+        commit.check()
+
+    def test_commit_with_nonsensical_timezone(self):
+        """Timezone is 'UTC + 5 hours and 75 minutes'."""
+        author_line = (
+            b'acpmasquerade <d@picovico.com> 1460127297 +0575'
+        )
+        expected_identity = b'acpmasquerade <d@picovico.com>'
+        expected_time = 1460127297
+        expected_timezone = +6 * 60 * 60 + 15 * 60
+        commit = Commit.from_string(self.make_commit_text(author=author_line))
+
+        # The commit parses properly
+        self.assertEqual(commit.author, expected_identity)
+        self.assertEqual(commit.author_time, expected_time)
+        self.assertEqual(commit.author_timezone, expected_timezone)
+
+        commit.check()
+
     def test_mangled_author_line(self):
         """Mangled author line should successfully parse"""
         author_line = (
@@ -722,10 +819,32 @@ def test_mangled_author_line(self):
             b'Karl MacMillan <kmacmill@redhat.com> <"Karl MacMillan '
             b'<kmacmill@redhat.com>">'
         )
+        expected_time = 1197475547
+        expected_timezone = -5 * 60 * 60
+        commit = Commit.from_string(self.make_commit_text(author=author_line))
+
+        # The commit parses properly
+        self.assertEqual(commit.author, expected_identity)
+        self.assertEqual(commit.author_time, expected_time)
+        self.assertEqual(commit.author_timezone, expected_timezone)
+
+        # But the check fails because the author identity is bogus
+        with self.assertRaises(ObjectFormatException):
+            commit.check()
+
+    def test_author_line_missing_brackets(self):
+        author_line = (
+            b'kapil.foss@gmail.com 1297013737 -0500'
+        )
+        expected_identity = b'kapil.foss@gmail.com'
+        expected_time = 1297013737
+        expected_timezone = -5 * 60 * 60
         commit = Commit.from_string(self.make_commit_text(author=author_line))
 
         # The commit parses properly
         self.assertEqual(commit.author, expected_identity)
+        self.assertEqual(commit.author_time, expected_time)
+        self.assertEqual(commit.author_timezone, expected_timezone)
 
         # But the check fails because the author identity is bogus
         with self.assertRaises(ObjectFormatException):