diff --git a/frontend/src/components/signals/BacktestPanel.tsx b/frontend/src/components/signals/BacktestPanel.tsx
index 264533f..58f2808 100644
--- a/frontend/src/components/signals/BacktestPanel.tsx
+++ b/frontend/src/components/signals/BacktestPanel.tsx
@@ -181,7 +181,10 @@ export function BacktestPanel() {
               </table>
             </div>
 
-            {report.sweep && report.sweep.length > 0 && (
+            {/* Guard on the new field so a stale cached report (pre-momentum,
+                with min_expected_value rows) hides the sweep instead of crashing
+                the whole page. Re-running the backtest repopulates it. */}
+            {report.sweep && report.sweep.length > 0 && report.sweep[0].min_momentum_percentile != null && (
               <div>
                 <p className="mb-2 text-xs font-medium uppercase tracking-widest text-gray-500">
                   Momentum-percentile sweep