diff --git a/signal_bot/stats/backfill.py b/signal_bot/stats/backfill.py
index 866cf24..d801023 100644
--- a/signal_bot/stats/backfill.py
+++ b/signal_bot/stats/backfill.py
@@ -28,10 +28,16 @@ if TYPE_CHECKING:
     from signal_bot.store import Store
 
 BACKFILL_KEY: Final = "backfill_day"
-# Noon: a backfilled event has no real hour, and midnight would look like a
-# deliberate reading rather than an absent one. The day is marked anyway, so
-# nothing that cares about hours will read these.
-BACKFILL_HOUR: Final = 12
+# -1, because a backfilled event has no hour at all and any value in 0..23 is
+# a lie that reads as data. This started as 12, on the reasoning that the day
+# is marked so "nothing that cares about hours will read these" -- and then
+# favourite_hour did, and told all seven people their favourite hour was
+# 12:00, because 319 synthetic noons outweighed every real evening.
+#
+# The lesson is in the type, not in a comment: an absent value must not be
+# spellable as a present one. Hour queries filter `local_hour >= 0`, so
+# forgetting to exclude the backfilled day can no longer invent an answer.
+UNKNOWN_HOUR: Final = -1
 
 
 def has_legacy_counter(store: Store) -> bool:
@@ -77,7 +83,7 @@ def seed_from_counter(store: Store, day: str) -> dict[str, int]:
                     display_name=row["display_name"],
                     sent_at_ms=index + 1,
                     day=day,
-                    local_hour=BACKFILL_HOUR,
+                    local_hour=UNKNOWN_HOUR,
                 )
             )
         store.events.note_person(group_id, row["uuid"], row["display_name"], "", day)
diff --git a/signal_bot/stats/curiosities.py b/signal_bot/stats/curiosities.py
index 3201314..bfef950 100644
--- a/signal_bot/stats/curiosities.py
+++ b/signal_bot/stats/curiosities.py
@@ -198,6 +198,7 @@ def night_owl(facts: DayFacts) -> Highlight | None:
         SELECT display_name, local_hour
         FROM message_events
         WHERE group_id = ? AND day = ? AND local_hour BETWEEN ? AND ?
+          AND local_hour >= 0
         ORDER BY local_hour DESC, sent_at_ms DESC LIMIT 1
         """,
         (facts.group_id, facts.day, 0, NIGHT_OWL_HOUR),
diff --git a/signal_bot/stats/render_extra.py b/signal_bot/stats/render_extra.py
index d3a1a22..8037ba4 100644
--- a/signal_bot/stats/render_extra.py
+++ b/signal_bot/stats/render_extra.py
@@ -174,12 +174,17 @@ def render_me(
 
 
 def favourite_hour(events: EventStore, group_id: str, uuid: str) -> int | None:
-    """The hour somebody writes most in, or None if they never have."""
+    """The hour somebody writes most in, or None when nothing is known.
+
+    Skips rows whose hour is UNKNOWN_HOUR. Those are backfilled from a counter
+    that had no timestamps, and counting them told every member of the group
+    that they write most at noon.
+    """
     row = events.connection.execute(
         """
         SELECT local_hour, COUNT(*) AS messages
         FROM message_events
-        WHERE group_id = ? AND uuid = ?
+        WHERE group_id = ? AND uuid = ? AND local_hour >= 0
         GROUP BY local_hour
         ORDER BY messages DESC, local_hour ASC
         LIMIT 1
diff --git a/tests/test_stats_backfill.py b/tests/test_stats_backfill.py
index 36b3d96..9fa6292 100644
--- a/tests/test_stats_backfill.py
+++ b/tests/test_stats_backfill.py
@@ -6,7 +6,7 @@ from __future__ import annotations
 from typing import TYPE_CHECKING
 
 from signal_bot.stats.backfill import (
-    BACKFILL_HOUR,
+    UNKNOWN_HOUR,
     backfilled_day,
     has_legacy_counter,
     seed_from_counter,
@@ -94,7 +94,12 @@ def test_seeded_people_are_known_to_the_roster(store: Store) -> None:
 
 
 def test_seeded_events_carry_no_invented_detail(store: Store) -> None:
-    """No hours, no lengths, no media -- the counter knew none of them."""
+    """No hours, no lengths, no media -- the counter knew none of them.
+
+    The hour is -1 rather than any real hour. It was noon once, and
+    favourite_hour then told all seven people they wrote most at midday: 319
+    synthetic noons outweighed every genuine evening.
+    """
     give_legacy_counter(store, [(GROUP, "u1", "Ala", 2)])
     seed_from_counter(store, DAY)
     rows = store.events.connection.execute(
@@ -102,7 +107,7 @@ def test_seeded_events_carry_no_invented_detail(store: Store) -> None:
     ).fetchall()
     assert len(rows) == 2
     for row in rows:
-        assert row["local_hour"] == BACKFILL_HOUR
+        assert row["local_hour"] == UNKNOWN_HOUR
         assert (row["char_len"], row["media_count"], row["is_command"]) == (0, 0, 0)
 
 
diff --git a/tests/test_stats_commands.py b/tests/test_stats_commands.py
index 9a25ce4..5cdde18 100644
--- a/tests/test_stats_commands.py
+++ b/tests/test_stats_commands.py
@@ -12,9 +12,10 @@ from signal_bot.animals import load_aliases
 from signal_bot.folding import fold
 from signal_bot.registry import CommandRegistry
 from signal_bot.stats import periods
-from signal_bot.stats.backfill import BACKFILL_KEY
+from signal_bot.stats.backfill import BACKFILL_KEY, seed_from_counter
 from signal_bot.stats.commands import HANDLERS, register_stats_commands
 from tests.stats_seed import GROUP, IGA, KUHY, MITHRA, Shape, wrote
+from tests.test_stats_backfill import LEGACY as LEGACY_COUNTER
 
 if TYPE_CHECKING:
     from signal_bot.store import Store
@@ -44,6 +45,17 @@ class FakeContext:
         self.replies.append(text)
 
 
+def seed_from_counter_rows(store: Store, uuid: str, name: str, count: int) -> None:
+    """Seed a pre-0.1.0 counter and carry it over, as the migration did."""
+    store.events.connection.executescript(LEGACY_COUNTER)
+    store.events.connection.execute(
+        "INSERT INTO message_counts (group_id, uuid, display_name, count) VALUES (?, ?, ?, ?)",
+        (GROUP, uuid, name, count),
+    )
+    store.events.connection.commit()
+    seed_from_counter(store, "2026-08-01")
+
+
 async def run(store: Store, name: str, uuid: str = KUHY[0]) -> str:
     """Run one command and return what it said."""
     ctx = FakeContext(store=store, message=Sender(source_uuid=uuid))
@@ -172,6 +184,31 @@ async def test_records_skips_somebody_with_no_days_left_after_exclusions(
     assert "Basia" not in rendered
 
 
+async def test_the_backfilled_day_cannot_invent_a_favourite_hour(
+    store: Store,
+) -> None:
+    """The 0.1.1 bug: everybody's favourite hour came out as 12:00.
+
+    The backfilled counter had no hours, and the placeholder was noon -- so
+    for every person the 319 seeded rows outvoted every real evening, and
+    !ja told each of them the same thing.
+    """
+    seed_from_counter_rows(store, KUHY[0], KUHY[1], 300)
+    wrote(store, "2026-08-15", KUHY, 3, Shape(hour=21))
+    answer = await run(store, "stats_me")
+    assert "między 21:00 a 22:00" in answer
+    assert "12:00" not in answer
+
+
+async def test_somebody_with_only_backfilled_messages_has_no_hour(
+    store: Store,
+) -> None:
+    """Nothing is known about when they wrote, so the line is omitted."""
+    seed_from_counter_rows(store, KUHY[0], KUHY[1], 5)
+    answer = await run(store, "stats_me")
+    assert "Najczęściej piszesz" not in answer
+
+
 async def test_weekdays_marks_today(store: Store) -> None:
     wrote(store, TODAY, MITHRA, 5)
     assert "← dziś" in await run(store, "stats_weekdays")