diff --git a/backend/services/infonet/tests/test_snapshot_invalid_numerics.py b/backend/services/infonet/tests/test_snapshot_invalid_numerics.py
new file mode 100644
index 0000000..d727e16
--- /dev/null
+++ b/backend/services/infonet/tests/test_snapshot_invalid_numerics.py
@@ -0,0 +1,70 @@
+"""Regression coverage for malformed/non-finite market snapshot inputs."""
+
+import math
+
+import pytest
+
+from services.infonet.markets.snapshot import build_snapshot, find_snapshot
+
+
+def _prediction(node, side, stake, *, timestamp, sequence):
+    payload = {"market_id": "m1", "side": side}
+    if stake is not None:
+        payload["stake_amount"] = stake
+    return {
+        "event_type": "prediction_place",
+        "node_id": node,
+        "timestamp": timestamp,
+        "sequence": sequence,
+        "payload": payload,
+    }
+
+
+def test_nonfinite_paid_stake_does_not_poison_snapshot():
+    chain = [
+        _prediction("alice", "yes", None, timestamp=100.0, sequence=1),
+        _prediction("mallory", "no", float("inf"), timestamp=101.0, sequence=2),
+    ]
+
+    snapshot = build_snapshot("m1", chain, frozen_at=200.0)
+
+    assert snapshot["frozen_participant_count"] == 1
+    assert snapshot["frozen_predictor_ids"] == ["alice"]
+    assert snapshot["frozen_total_stake"] == 0.0
+    assert snapshot["frozen_probability_state"] == {"yes": 1.0, "no": 0.0}
+    assert all(math.isfinite(v) for v in snapshot["frozen_probability_state"].values())
+
+
+def test_malformed_ordering_metadata_does_not_break_snapshot_build():
+    chain = [
+        _prediction("alice", "yes", 5.0, timestamp="bad", sequence="bad"),
+        _prediction("bob", "no", 5.0, timestamp=100.0, sequence=1),
+    ]
+
+    snapshot = build_snapshot("m1", chain, frozen_at=200.0)
+
+    assert snapshot["frozen_participant_count"] == 2
+    assert snapshot["frozen_total_stake"] == 10.0
+    assert snapshot["frozen_probability_state"] == {"yes": 0.5, "no": 0.5}
+
+
+def test_invalid_snapshot_ordering_does_not_outrank_valid_snapshot():
+    invalid = {
+        "event_type": "market_snapshot",
+        "timestamp": "bad",
+        "sequence": "bad",
+        "payload": {"market_id": "m1", "marker": "invalid"},
+    }
+    valid = {
+        "event_type": "market_snapshot",
+        "timestamp": 100.0,
+        "sequence": 1,
+        "payload": {"market_id": "m1", "marker": "valid"},
+    }
+
+    assert find_snapshot("m1", [invalid, valid])["marker"] == "valid"
+
+
+def test_nonfinite_frozen_at_is_rejected():
+    with pytest.raises(ValueError, match="frozen_at must be finite"):
+        build_snapshot("m1", [], frozen_at=float("nan"))