diff --git a/tests/test_voiceeval.py b/tests/test_voiceeval.py
index b9aa363..098d314 100644
--- a/tests/test_voiceeval.py
+++ b/tests/test_voiceeval.py
@@ -122,6 +122,52 @@ def test_prompt_response_is_not_flagged():
     assert "slow_response" not in _codes(inter)
 
 
+def test_negative_latency_out_of_order_clocks_produce_invalid_timing_finding():
+    """Negative gap (agent starting before caller finishes beyond normal overlap) must be flagged."""
+    inter = Interaction(
+        id="t",
+        turns=[
+            _t("user", "hello", 0, 2.0, truth="hello"),
+            _t("agent", "Hi there.", 0.5, 2.5),
+        ],
+    )
+    findings = [f for f in analyse(inter) if f.check == "invalid_timing"]
+    assert len(findings) == 1
+    assert findings[0].severity == "high"
+    assert findings[0].turn_index == 1
+
+
+def test_out_of_order_turn_timestamps_flagged_as_invalid_timing():
+    """Corrupt fixture where clocks jump backwards (agent turn starts before user turn started)."""
+    inter = Interaction(
+        id="t",
+        turns=[
+            _t("user", "hello", 10.0, 12.0, truth="hello"),
+            _t("agent", "Hi there.", 5.0, 7.0),
+        ],
+    )
+    findings = [f for f in analyse(inter) if f.check == "invalid_timing"]
+    assert len(findings) == 1
+    assert findings[0].severity == "high"
+    assert findings[0].turn_index == 1
+    assert "7.0s before user turn ended" in findings[0].message
+
+
+
+def test_small_conversational_overlap_in_response_is_not_flagged():
+    """A ~200ms overlap when the agent starts replying is normal turn-taking, not a fault."""
+    inter = Interaction(
+        id="t",
+        turns=[
+            _t("user", "hello", 0, 2.0, truth="hello"),
+            _t("agent", "Hi there.", 1.8, 3.0),
+        ],
+    )
+    assert "invalid_timing" not in _codes(inter)
+    assert "slow_response" not in _codes(inter)
+
+
+
 def test_talking_over_user_is_caught():
     inter = Interaction(
         id="t",
diff --git a/voiceeval/checks.py b/voiceeval/checks.py
index f94a263..98779a8 100644
--- a/voiceeval/checks.py
+++ b/voiceeval/checks.py
@@ -21,7 +21,7 @@
 import re
 from dataclasses import dataclass
 
-from .turns import Interaction, Turn
+from .turns import Interaction
 
 
 @dataclass
@@ -160,6 +160,16 @@ def check_latency(inter: Interaction, budget_s: float = 1.5) -> list[Finding]:
                     idx,
                 )
             )
+        elif gap < -0.3:
+            idx = inter.turns.index(agent_turn)
+            out.append(
+                Finding(
+                    "invalid_timing",
+                    "high",
+                    f"Agent turn started {-gap:.1f}s before user turn ended.",
+                    idx,
+                )
+            )
     return out