diff --git a/swh/model/hypothesis_strategies.py b/swh/model/hypothesis_strategies.py
--- a/swh/model/hypothesis_strategies.py
+++ b/swh/model/hypothesis_strategies.py
@@ -131,6 +131,18 @@
     min_seconds = datetime.datetime.min.replace(
         tzinfo=datetime.timezone.utc
     ).timestamp()
+
+    # in Python 3.9, datetime.datetime.max is 9999-12-31T23:59:59.999999, which
+    # means its .timestamp() is 253402300799.999999 in UTC. Unfortunately, because of
+    # flotting-point loss of precision, this is rounded up to 253402300800.0, which
+    # is the timestamp of 10000-01-01T00:00:00 in UTC, which cannot be passed to
+    # datetime.datetime.fromtimestamp because it overflows.
+    # To work around this issue, we move from max_seconds and min_seconds one second
+    # closer to Epoch, which is more than enough (actually, subtracting 20ms from
+    # max_seconds is enough).
+    max_seconds -= 1
+    min_seconds += 1
+
     defaults = dict(
         seconds=integers(min_seconds, max_seconds),
         microseconds=integers(0, 1000000 - 1),