diff --git a/crdt-sync/crdt_sync/_firebase_auth.py b/crdt-sync/crdt_sync/_firebase_auth.py
index 85c22d0..81afd2a 100644
--- a/crdt-sync/crdt_sync/_firebase_auth.py
+++ b/crdt-sync/crdt_sync/_firebase_auth.py
@@ -161,7 +161,7 @@ class FileCredentialStore:
 
 
 def _utcnow() -> dt.datetime:
-    return dt.datetime.now(dt.UTC)
+    return dt.datetime.now(dt.timezone.utc)
 
 
 class FirebaseTokenProvider:
diff --git a/crdt-sync/crdt_sync/tests/test_firebase.py b/crdt-sync/crdt_sync/tests/test_firebase.py
index ca7a71a..b6eb24c 100644
--- a/crdt-sync/crdt_sync/tests/test_firebase.py
+++ b/crdt-sync/crdt_sync/tests/test_firebase.py
@@ -56,7 +56,7 @@ def _auth(*, signed_in: bool = True) -> FirebaseTokenProvider:
         FirebaseCredentials(
             id_token=_FAKE_ID,
             refresh_token=_FAKE_REFRESH,
-            expires_at=dt.datetime(2099, 1, 1, tzinfo=dt.UTC),
+            expires_at=dt.datetime(2099, 1, 1, tzinfo=dt.timezone.utc),
         )
         if signed_in
         else None
diff --git a/crdt-sync/crdt_sync/tests/test_firebase_auth.py b/crdt-sync/crdt_sync/tests/test_firebase_auth.py
index 799ba97..8409aa0 100644
--- a/crdt-sync/crdt_sync/tests/test_firebase_auth.py
+++ b/crdt-sync/crdt_sync/tests/test_firebase_auth.py
@@ -27,7 +27,7 @@ from crdt_sync import _firebase_auth as fa
 if TYPE_CHECKING:
     from pathlib import Path
 
-_NOW = dt.datetime(2026, 8, 3, 12, tzinfo=dt.UTC)
+_NOW = dt.datetime(2026, 8, 3, 12, tzinfo=dt.timezone.utc)
 
 # Fixture values referenced through names ruff's hardcoded-credential checks
 # (S105-S107) do not key off. Comparing an attribute called `id_token` to a