diff --git a/swh/deposit/tests/api/test_deposit_private_read_metadata.py b/swh/deposit/tests/api/test_deposit_private_read_metadata.py
--- a/swh/deposit/tests/api/test_deposit_private_read_metadata.py
+++ b/swh/deposit/tests/api/test_deposit_private_read_metadata.py
@@ -83,12 +83,10 @@
                 "author": SWH_PERSON,
                 "committer": SWH_PERSON,
                 "committer_date": {
-                    "negative_utc": False,
                     "offset": 0,
                     "timestamp": {"microseconds": 0, "seconds": 1507389428},
                 },
                 "author_date": {
-                    "negative_utc": False,
                     "offset": 0,
                     "timestamp": {"microseconds": 0, "seconds": 1507389428},
                 },
@@ -157,12 +155,10 @@
                 "author": SWH_PERSON,
                 "committer": SWH_PERSON,
                 "committer_date": {
-                    "negative_utc": False,
                     "offset": 0,
                     "timestamp": {"microseconds": 0, "seconds": 1507389428},
                 },
                 "author_date": {
-                    "negative_utc": False,
                     "offset": 0,
                     "timestamp": {"microseconds": 0, "seconds": 1507389428},
                 },
@@ -233,12 +229,10 @@
                 "author": SWH_PERSON,
                 "committer": SWH_PERSON,
                 "committer_date": {
-                    "negative_utc": False,
                     "offset": 120,
                     "timestamp": {"microseconds": 0, "seconds": 1493820527},
                 },
                 "author_date": {
-                    "negative_utc": False,
                     "offset": 0,
                     "timestamp": {"microseconds": 0, "seconds": 1507389428},
                 },
@@ -293,12 +287,10 @@
                 "author": SWH_PERSON,
                 "committer": SWH_PERSON,
                 "committer_date": {
-                    "negative_utc": False,
                     "offset": 0,
                     "timestamp": {"microseconds": 0, "seconds": 1459900800},
                 },
                 "author_date": {
-                    "negative_utc": False,
                     "offset": 0,
                     "timestamp": {"microseconds": 0, "seconds": 1459900800},
                 },
@@ -366,12 +358,10 @@
                 "author": SWH_PERSON,
                 "committer": SWH_PERSON,
                 "committer_date": {
-                    "negative_utc": False,
                     "offset": 120,
                     "timestamp": {"microseconds": 0, "seconds": 1493820527},
                 },
                 "author_date": {
-                    "negative_utc": False,
                     "offset": 120,
                     "timestamp": {"microseconds": 0, "seconds": 1428332927},
                 },
@@ -450,12 +440,10 @@
                 "author": SWH_PERSON,
                 "committer": SWH_PERSON,
                 "committer_date": {
-                    "negative_utc": False,
                     "offset": 0,
                     "timestamp": {"microseconds": 0, "seconds": 1507389428},
                 },
                 "author_date": {
-                    "negative_utc": False,
                     "offset": 0,
                     "timestamp": {"microseconds": 0, "seconds": 1507389428},
                 },
diff --git a/swh/deposit/tests/loader/data/https_deposit.softwareheritage.org/1_private_test_999_meta b/swh/deposit/tests/loader/data/https_deposit.softwareheritage.org/1_private_test_999_meta
--- a/swh/deposit/tests/loader/data/https_deposit.softwareheritage.org/1_private_test_999_meta
+++ b/swh/deposit/tests/loader/data/https_deposit.softwareheritage.org/1_private_test_999_meta
@@ -40,7 +40,6 @@
           "email": "robot@softwareheritage.org"
         },
         "committer_date": {
-            "negative_utc": "false",
             "offset": 0,
             "timestamp": {
                 "microseconds": 0,
@@ -48,7 +47,6 @@
             }
         },
         "date": {
-            "negative_utc": "false",
             "offset": 0,
             "timestamp": {"microseconds": 0, "seconds": 1507389428}
         },
diff --git a/swh/deposit/tests/test_utils.py b/swh/deposit/tests/test_utils.py
--- a/swh/deposit/tests/test_utils.py
+++ b/swh/deposit/tests/test_utils.py
@@ -120,7 +120,6 @@
 
     assert actual_date == {
         "timestamp": {"microseconds": 0, "seconds": 1507766400},
-        "negative_utc": False,
         "offset": 0,
     }
 
@@ -132,7 +131,6 @@
 
     assert actual_date == {
         "timestamp": {"microseconds": 0, "seconds": 1528736522},
-        "negative_utc": False,
         "offset": 0,
     }
 
@@ -145,7 +143,6 @@
     assert actual_date == {
         "timestamp": {"seconds": 1483228800, "microseconds": 0},
         "offset": 0,
-        "negative_utc": False,
     }
 
 
diff --git a/swh/deposit/utils.py b/swh/deposit/utils.py
--- a/swh/deposit/utils.py
+++ b/swh/deposit/utils.py
@@ -109,15 +109,12 @@
     if isinstance(date, str):
         date = iso8601.parse_date(date)
 
-    d = TimestampWithTimezone.from_dict(date).to_dict()
+    tstz = TimestampWithTimezone.from_dict(date)
 
-    # Workaround while we migrate from storing offsets as (int, bool) to bytes.
-    # When the migration is done, remove this pop().
-    # offset_bytes will also need to be converted to a string (which is fine because
-    # it is always a well-formed offset)
-    d.pop("offset_bytes", None)
-
-    return d
+    return {
+        "timestamp": tstz.timestamp.to_dict(),
+        "offset": tstz.offset,
+    }
 
 
 def compute_metadata_context(swhid_reference: QualifiedSWHID) -> Dict[str, Any]: