diff --git a/src/services/inventoryService.ts b/src/services/inventoryService.ts
index 5665824f..f99ab6c2 100644
--- a/src/services/inventoryService.ts
+++ b/src/services/inventoryService.ts
@@ -126,6 +126,7 @@ export const generateRewardSeed = (): bigint => {
     let seed = (BigInt(hiDword) << 32n) | BigInt(loDword);
     if (Math.random() < 0.5) {
         seed *= -1n;
+        seed -= 1n;
     }
     return seed;
 };