diff --git a/src/sim/knowledge.js b/src/sim/knowledge.js
index 8f62e0c..7bde6fa 100644
--- a/src/sim/knowledge.js
+++ b/src/sim/knowledge.js
@@ -13,7 +13,8 @@ export function playerKnownPrices(world, planetId) {
   const book = p.priceBook[planetId] ?? null;
   let best = book;
   if (news && (!best || news.time > best.time)) best = news;
-  if (best && (!book || best.time > book.time)) p.priceBook[planetId] = best;
+  // Copy the envelope so the price book never aliases NewsLedger's stored snapshots.
+  if (best && (!book || best.time > book.time)) p.priceBook[planetId] = { time: best.time, prices: best.prices };
   return best ? { time: best.time, prices: best.prices, ageDays: world.t - best.time } : null;
 }