diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9a3d0ff..c426878 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -29,6 +29,8 @@ and this project adheres to
 - Fix leaked file handles in tests using context managers ([b66a6f5], [#25])
 - Fix `Decimal.normalize()` stripping trailing zeros, breaking round-trip
   serialization; add regression test ([28c76f1], [0130743], [#28])
+- Add return type annotations to test functions for mypy compliance
+  ([cd74b55], [#43])
 - Fix typo in test name: `test_l9events_form_ip4scout` ->
   `test_l9events_from_ip4scout` ([0d8736e], [#27])
 
@@ -154,6 +156,7 @@ and this project adheres to
 
 <!-- Commit links -->
 
+[cd74b55]: https://github.com/LeakIX/l9format-python/commit/cd74b55
 [0130743]: https://github.com/LeakIX/l9format-python/commit/0130743
 [28c76f1]: https://github.com/LeakIX/l9format-python/commit/28c76f1
 [b66a6f5]: https://github.com/LeakIX/l9format-python/commit/b66a6f5
@@ -230,3 +233,4 @@ and this project adheres to
 [#33]: https://github.com/LeakIX/l9format-python/issues/33
 [#25]: https://github.com/LeakIX/l9format-python/issues/25
 [#35]: https://github.com/LeakIX/l9format-python/issues/35
+[#43]: https://github.com/LeakIX/l9format-python/issues/43
diff --git a/tests/test_l9format.py b/tests/test_l9format.py
index 035f8ca..573e848 100644
--- a/tests/test_l9format.py
+++ b/tests/test_l9format.py
@@ -12,7 +12,7 @@
 ]
 
 
-def test_l9event_json_from_reference_repository():
+def test_l9event_json_from_reference_repository() -> None:
     path = TESTS_DIR / "l9event.json"
     with open(path) as f:
         c = json.load(f)
@@ -55,7 +55,7 @@ def test_l9event_json_from_reference_repository():
     ]
 
 
-def test_l9events_from_ip4scout():
+def test_l9events_from_ip4scout() -> None:
     for path in IP4SCOUT_FILES:
         with open(path) as f:
             c = json.load(f)
@@ -68,7 +68,7 @@ def test_l9events_from_ip4scout():
         assert len(event.port) > 0
 
 
-def test_iso8601_nanosecond_parsing():
+def test_iso8601_nanosecond_parsing() -> None:
     """
     Test ISO8601 datetime parsing with nanosecond precision.
 
@@ -89,7 +89,7 @@ def test_iso8601_nanosecond_parsing():
     assert event.time.second == 36
 
 
-def test_all_models_importable_from_package():
+def test_all_models_importable_from_package() -> None:
     """Verify all public models are importable from the l9format package."""
     import l9format