diff --git a/status_model.py b/status_model.py
index 089c9ae..6c1fa10 100644
--- a/status_model.py
+++ b/status_model.py
@@ -38,7 +38,7 @@ def is_status_stale(
 
     current_time = now or datetime.now()
     age_seconds = (current_time - updated_at).total_seconds()
-    return age_seconds > stale_after_seconds
+    return age_seconds < 0 or age_seconds > stale_after_seconds
 
 
 def default_status() -> Dict[str, Any]:
diff --git a/tests/test_status_model.py b/tests/test_status_model.py
index c08ea47..a72feb0 100644
--- a/tests/test_status_model.py
+++ b/tests/test_status_model.py
@@ -55,6 +55,14 @@ def test_is_status_stale_uses_supplied_threshold(self):
         self.assertTrue(status_model.is_status_stale(status, 60))
         self.assertFalse(status_model.is_status_stale(status, 300))
 
+    def test_is_status_stale_treats_future_time_as_untrusted(self):
+        now = datetime(2026, 5, 29, 10, 0, 0)
+        future_status = {
+            "updated_at": (now + timedelta(minutes=5)).strftime("%Y-%m-%d %H:%M:%S")
+        }
+
+        self.assertTrue(status_model.is_status_stale(future_status, 900, now=now))
+
 
 if __name__ == "__main__":
     unittest.main()