diff --git a/leapseconddata.py b/leapseconddata/__init__.py
similarity index 90%
rename from leapseconddata.py
rename to leapseconddata/__init__.py
index 556c927..3565831 100755
--- a/leapseconddata.py
+++ b/leapseconddata/__init__.py
@@ -359,38 +359,3 @@ class LeapSecondData(_LeapSecondData):
                 )
 
         return LeapSecondData(leap_seconds, valid_until, last_updated)
-
-
-def main() -> None:
-    """When run as a main program, print some information about leap seconds"""
-    logging.getLogger().setLevel(logging.INFO)
-    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()}")
-    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()}")
-
-    when_tai = lsd.to_tai(when)
-    when_rt = lsd.tai_to_utc(when_tai)
-    print(f"{when:%Y-%m-%d %H:%M:%S} UTC -> {when_tai:%Y-%m-%d %H:%M:%S} TAI")
-    print(f"{when_tai:%Y-%m-%d %H:%M:%S} TAI -> {when_rt:%Y-%m-%d %H:%M:%S} UTC")
-    print(f"is leap second? {lsd.is_leap_second(when)}")
-
-    u = datetime.datetime(
-        1999, 1, 1, tzinfo=datetime.timezone.utc
-    ) - datetime.timedelta(seconds=2)
-    t = lsd.to_tai(u)
-
-    print("replaying leapsecond at end of 1998")
-    for _ in range(5):
-        print(
-            f"{u:%Y-%m-%d %H:%M:%S} UTC {'LS' if lsd.is_leap_second(u) else '  '} = {t:%Y-%m-%d %H:%M:%S} TAI {'LS' if lsd.is_leap_second(t) else '  '}"
-        )
-        t += datetime.timedelta(seconds=1)
-        u = lsd.tai_to_utc(t)
-
-
-if __name__ == "__main__":  # pragma no cover
-    main()
diff --git a/leapseconddata/__main__.py b/leapseconddata/__main__.py
new file mode 100644
index 0000000..69b347a
--- /dev/null
+++ b/leapseconddata/__main__.py
@@ -0,0 +1,48 @@
+# SPDX-FileCopyrightText: 2022 Jeff Epler
+#
+# SPDX-License-Identifier: GPL-3.0-only
+
+"""
+Smoke test program for leapseconddata
+
+If this was a useful program, it would be exposed as an entry point in setup.cfg.
+"""
+
+import datetime
+import logging
+from . import LeapSecondData
+
+
+def main() -> None:
+    """When run as a main program, print some information about leap seconds"""
+    logging.getLogger().setLevel(logging.INFO)
+    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()}")
+    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()}")
+
+    when_tai = lsd.to_tai(when)
+    when_rt = lsd.tai_to_utc(when_tai)
+    print(f"{when:%Y-%m-%d %H:%M:%S} UTC -> {when_tai:%Y-%m-%d %H:%M:%S} TAI")
+    print(f"{when_tai:%Y-%m-%d %H:%M:%S} TAI -> {when_rt:%Y-%m-%d %H:%M:%S} UTC")
+    print(f"is leap second? {lsd.is_leap_second(when)}")
+
+    u = datetime.datetime(
+        1999, 1, 1, tzinfo=datetime.timezone.utc
+    ) - datetime.timedelta(seconds=2)
+    t = lsd.to_tai(u)
+
+    print("replaying leapsecond at end of 1998")
+    for _ in range(5):
+        print(
+            f"{u:%Y-%m-%d %H:%M:%S} UTC {'LS' if lsd.is_leap_second(u) else '  '} = {t:%Y-%m-%d %H:%M:%S} TAI {'LS' if lsd.is_leap_second(t) else '  '}"
+        )
+        t += datetime.timedelta(seconds=1)
+        u = lsd.tai_to_utc(t)
+
+
+if __name__ == "__main__":  # pragma no cover
+    main()
diff --git a/leapseconddata/py.typed b/leapseconddata/py.typed
new file mode 100644
index 0000000..e69de29
diff --git a/setup.cfg b/setup.cfg
index 8e8b4a6..1510fb4 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -22,5 +22,10 @@ classifiers =
     Operating System :: OS Independent
 
 [options]
+package_dir =
+    =.
 python_requires = >=3.7
-py_modules = leapseconddata
+packages = leapseconddata
+
+[options.package_data]
+leapseconddata = py.typed
diff --git a/testleapseconddata.py b/testleapseconddata.py
index 80f6f0d..3ba1301 100644
--- a/testleapseconddata.py
+++ b/testleapseconddata.py
@@ -9,6 +9,7 @@
 import datetime
 import unittest
 import leapseconddata
+import leapseconddata.__main__
 
 db = leapseconddata.LeapSecondData.from_standard_source()
 
@@ -17,7 +18,7 @@ GMT1 = datetime.timezone(datetime.timedelta(seconds=3600), "GMT1")
 
 class LeapSecondDataTest(unittest.TestCase):
     def test_main(self) -> None:  # pylint: disable=no-self-use
-        leapseconddata.main()
+        leapseconddata.__main__.main()
 
     def test_corrupt(self) -> None:
         self.assertRaises(