diff --git a/sickdays/sickdays/_store.py b/sickdays/sickdays/_store.py
index eb9a2d1..7acdae5 100644
--- a/sickdays/sickdays/_store.py
+++ b/sickdays/sickdays/_store.py
@@ -36,7 +36,7 @@ def _read(path: Path) -> Log:
         text = path.read_text(encoding="utf-8")
     except FileNotFoundError:
         return {}
-    except OSError as exc:
+    except (OSError, UnicodeDecodeError) as exc:
         msg = f"the sick-day pool {path} cannot be read: {exc}"
         raise UnreadablePoolError(msg) from exc
     try:
diff --git a/sickdays/sickdays/tests/test_store.py b/sickdays/sickdays/tests/test_store.py
index 79644da..bb4e754 100644
--- a/sickdays/sickdays/tests/test_store.py
+++ b/sickdays/sickdays/tests/test_store.py
@@ -74,3 +74,14 @@ def test_writers_refuse_rather_than_overwrite_a_corrupt_pool(state_dir: Path) ->
     with pytest.raises(UnreadablePoolError):
         import_legacy([TODAY])
     assert pool.read_text(encoding="utf-8") == "{not json"
+
+
+def test_a_non_utf8_pool_fails_closed_and_refuses_writers(
+    state_dir: Path, caplog: pytest.LogCaptureFixture
+) -> None:
+    (state_dir / "sick_days.json").write_bytes(b"\xff\xfe\x00junk")
+    with caplog.at_level("WARNING"):
+        assert not is_sick_day(TODAY)
+    assert "cannot be read" in caplog.text
+    with pytest.raises(UnreadablePoolError):
+        add_sick_day(TODAY, now=TODAY)