diff --git a/leapseconddata/__init__.py b/leapseconddata/__init__.py
index 9379422..04dca8c 100755
--- a/leapseconddata/__init__.py
+++ b/leapseconddata/__init__.py
@@ -29,22 +29,20 @@
 import re
 import urllib.request
 from dataclasses import dataclass, field
-from typing import BinaryIO, List, NamedTuple, Optional, Union
+from typing import BinaryIO, List, Optional, Union
 
 tai = datetime.timezone(datetime.timedelta(0), "TAI")
 
 NTP_EPOCH = datetime.datetime(1900, 1, 1, tzinfo=datetime.timezone.utc)
 
-LeapSecondInfo = NamedTuple(
-    "LeapSecondInfo", (("start", datetime.datetime), ("tai", datetime.timedelta))
-)
 
-LeapSecondInfo.start.__doc__ = """The UTC timestamp just after the insertion of the leap second.
+@dataclass(frozen=True)
+class LeapSecondInfo:
+    start: datetime.datetime
+    """The UTC timestamp just after the insertion of the leap second."""
 
-The leap second is actually the 60th second of the previous minute"""
-LeapSecondInfo.tai.__doc__ = (
+    tai_offset: datetime.timedelta
     """The new TAI-UTC offset.  Positive numbers indicate that TAI is ahead of UTC"""
-)
 
 
 class ValidityError(ValueError):
@@ -130,13 +128,14 @@ def tai_offset(
             return datetime.timedelta(0)
 
         old_tai = datetime.timedelta()
-        for start, tai_offset in self.leap_seconds:
+        for leap_second in self.leap_seconds:
+            start = leap_second.start
             if is_tai:
-                start += tai_offset - datetime.timedelta(seconds=1)
+                start += leap_second.tai_offset - datetime.timedelta(seconds=1)
             if when < start:
                 return old_tai
-            old_tai = tai_offset
-        return self.leap_seconds[-1].tai
+            old_tai = leap_second.tai_offset
+        return self.leap_seconds[-1].tai_offset
 
     def to_tai(
         self, when: datetime.datetime, check_validity: bool = True
diff --git a/leapseconddata/__main__.py b/leapseconddata/__main__.py
index 0cf17ce..e333d2a 100644
--- a/leapseconddata/__main__.py
+++ b/leapseconddata/__main__.py
@@ -20,8 +20,8 @@ def main() -> None:
     lsd = LeapSecondData.from_standard_source()
     print(f"Last updated: {lsd.last_updated:%Y-%m-%d}")
     print(f"Valid until:  {lsd.valid_until:%Y-%m-%d}")
-    for when, offset in lsd.leap_seconds[-10:]:
-        print(f"{when:%Y-%m-%d}: {offset.total_seconds()}")
+    for leap_second in lsd.leap_seconds[-10:]:
+        print(f"{leap_second.start:%Y-%m-%d}: {leap_second.tai_offset.total_seconds()}")
     when = datetime.datetime(2011, 1, 1, tzinfo=datetime.timezone.utc)
     print(f"TAI-UTC on {when:%Y-%m-%d} was {lsd.tai_offset(when).total_seconds()}")