diff --git a/borg/helpers.py b/borg/helpers.py
index b342c60e0..15c01bb7c 100644
--- a/borg/helpers.py
+++ b/borg/helpers.py
@@ -681,11 +681,15 @@ def posix_acl_use_stored_uid_gid(acl):
 
 def safe_decode(s, coding='utf-8', errors='surrogateescape'):
     """decode bytes to str, with round-tripping "invalid" bytes"""
+    if s is None:
+        return None
     return s.decode(coding, errors)
 
 
 def safe_encode(s, coding='utf-8', errors='surrogateescape'):
     """encode str to bytes, with round-tripping "invalid" bytes"""
+    if s is None:
+        return None
     return s.encode(coding, errors)
 
 
diff --git a/borg/item.py b/borg/item.py
index 2bf9c650b..b0cbf12a3 100644
--- a/borg/item.py
+++ b/borg/item.py
@@ -1,5 +1,5 @@
 from .constants import ITEM_KEYS
-from .helpers import safe_encode, safe_decode, StableDict
+from .helpers import safe_encode, safe_decode, bigint_to_int, int_to_bigint, StableDict
 
 
 class PropDict:
@@ -112,22 +112,24 @@ class Item(PropDict):
 
     path = PropDict._make_property('path', str, 'surrogate-escaped str', encode=safe_encode, decode=safe_decode)
     source = PropDict._make_property('source', str, 'surrogate-escaped str', encode=safe_encode, decode=safe_decode)
-    user = PropDict._make_property('user', str, 'surrogate-escaped str', encode=safe_encode, decode=safe_decode)
-    group = PropDict._make_property('group', str, 'surrogate-escaped str', encode=safe_encode, decode=safe_decode)
     acl_access = PropDict._make_property('acl_access', str, 'surrogate-escaped str', encode=safe_encode, decode=safe_decode)
     acl_default = PropDict._make_property('acl_default', str, 'surrogate-escaped str', encode=safe_encode, decode=safe_decode)
     acl_extended = PropDict._make_property('acl_extended', str, 'surrogate-escaped str', encode=safe_encode, decode=safe_decode)
     acl_nfs4 = PropDict._make_property('acl_nfs4', str, 'surrogate-escaped str', encode=safe_encode, decode=safe_decode)
 
+    user = PropDict._make_property('user', (str, type(None)), 'surrogate-escaped str or None', encode=safe_encode, decode=safe_decode)
+    group = PropDict._make_property('group', (str, type(None)), 'surrogate-escaped str or None', encode=safe_encode, decode=safe_decode)
+
     mode = PropDict._make_property('mode', int)
     uid = PropDict._make_property('uid', int)
     gid = PropDict._make_property('gid', int)
-    atime = PropDict._make_property('atime', int)
-    ctime = PropDict._make_property('ctime', int)
-    mtime = PropDict._make_property('mtime', int)
     rdev = PropDict._make_property('rdev', int)
     bsdflags = PropDict._make_property('bsdflags', int)
 
+    atime = PropDict._make_property('atime', int, 'bigint', encode=int_to_bigint, decode=bigint_to_int)
+    ctime = PropDict._make_property('ctime', int, 'bigint', encode=int_to_bigint, decode=bigint_to_int)
+    mtime = PropDict._make_property('mtime', int, 'bigint', encode=int_to_bigint, decode=bigint_to_int)
+
     hardlink_master = PropDict._make_property('hardlink_master', bool)
 
     chunks = PropDict._make_property('chunks', list)
diff --git a/borg/testsuite/item.py b/borg/testsuite/item.py
index e41d6ae18..16e887cbb 100644
--- a/borg/testsuite/item.py
+++ b/borg/testsuite/item.py
@@ -63,6 +63,25 @@ def test_item_int_property():
         item.mode = "invalid"
 
 
+def test_item_bigint_property():
+    item = Item()
+    small, big = 42, 2 ** 65
+    item.atime = small
+    assert item.atime == small
+    assert item.as_dict() == {'atime': small}
+    item.atime = big
+    assert item.atime == big
+    assert item.as_dict() == {'atime': b'\0' * 8 + b'\x02'}
+
+
+def test_item_user_group_none():
+    item = Item()
+    item.user = None
+    assert item.user is None
+    item.group = None
+    assert item.group is None
+
+
 def test_item_se_str_property():
     # start simple
     item = Item()