diff --git a/tests/test_api.py b/tests/test_api.py
index 85cc33eae5..e4d1a4ef40 100755
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -258,6 +258,10 @@ def test_metadata_snapshot(self):
         snapshot.signed.update('role1', 2, 123, hashes)
         self.assertEqual(snapshot.signed.meta, fileinfo)
 
+        # Update only version. Length and hashes are optional.
+        snapshot.signed.update('role1', 3)
+        fileinfo['role1.json'] = {'version': 3}
+        self.assertEqual(snapshot.signed.meta, fileinfo)
 
     def test_metadata_timestamp(self):
         timestamp_path = os.path.join(
@@ -293,6 +297,10 @@ def test_metadata_timestamp(self):
         timestamp.signed.update(2, 520, hashes)
         self.assertEqual(timestamp.signed.meta['snapshot.json'], fileinfo)
 
+        # Update only version. Length and hashes are optional.
+        timestamp.signed.update(3)
+        fileinfo = {'version': 3}
+        self.assertEqual(timestamp.signed.meta['snapshot.json'], fileinfo)
 
     def test_metadata_root(self):
         root_path = os.path.join(
diff --git a/tuf/api/metadata.py b/tuf/api/metadata.py
index e28310ae56..c5fa78bff0 100644
--- a/tuf/api/metadata.py
+++ b/tuf/api/metadata.py
@@ -520,7 +520,7 @@ class Timestamp(Signed):
                         '<HASH ALGO 1>': '<SNAPSHOT METADATA FILE HASH 1>',
                         '<HASH ALGO 2>': '<SNAPSHOT METADATA FILE HASH 2>',
                         ...
-                    }
+                    } // optional
                 }
             }
 
@@ -557,14 +557,19 @@ def to_dict(self) -> Dict[str, Any]:
 
     # Modification.
     def update(
-        self, version: int, length: int, hashes: Mapping[str, Any]
+        self,
+        version: int,
+        length: Optional[int] = None,
+        hashes: Optional[Mapping[str, Any]] = None,
     ) -> None:
         """Assigns passed info about snapshot metadata to meta dict."""
-        self.meta["snapshot.json"] = {
-            "version": version,
-            "length": length,
-            "hashes": hashes,
-        }
+        self.meta["snapshot.json"] = {"version": version}
+
+        if length is not None:
+            self.meta["snapshot.json"]["length"] = length
+
+        if hashes is not None:
+            self.meta["snapshot.json"]["hashes"] = hashes
 
 
 class Snapshot(Signed):