diff --git a/pyproject.toml b/pyproject.toml
index f6f85d264b..875bedf95d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -54,6 +54,8 @@ dependencies = [
 	"PyQt6_WebEngine == 6.8.0",
 	"MacFSEvents == 0.8.4; sys_platform == 'darwin'",
 	"xxhash == 3.3.0",
+    "tzdata == 2025.2",
+    "tzlocal == 5.3.1",
 ]
 
 [project.urls]
diff --git a/src/calibre/utils/iso8601.py b/src/calibre/utils/iso8601.py
index 3a95946c81..c4d58cdfa3 100644
--- a/src/calibre/utils/iso8601.py
+++ b/src/calibre/utils/iso8601.py
@@ -3,11 +3,18 @@
 
 
 from datetime import datetime, timedelta, timezone
+from zoneinfo import ZoneInfo
+
+import tzlocal
 
 from calibre_extensions import speedup
 
 utc_tz = timezone.utc
-local_tz = datetime.now().astimezone().tzinfo
+try:
+    tz_name = tzlocal.get_localzone_name()
+    local_tz = ZoneInfo(tz_name)
+except Exception:
+    local_tz = datetime.now().astimezone().tzinfo
 UNDEFINED_DATE = datetime(101,1,1, tzinfo=utc_tz)