diff --git a/packages/taler-wallet-core/src/db.ts b/packages/taler-wallet-core/src/db.ts
index 597cdf5a5..a5ead4d64 100644
--- a/packages/taler-wallet-core/src/db.ts
+++ b/packages/taler-wallet-core/src/db.ts
@@ -2434,10 +2434,13 @@ export const WalletStoresV1 = {
     "planchets",
     describeContents<PlanchetRecord>({ keyPath: "coinPub" }),
     {
-      byGroupAndIndex: describeIndex("byGroupAndIndex", [
-        "withdrawalGroupId",
-        "coinIdx",
-      ]),
+      byGroupAndIndex: describeIndex(
+        "byGroupAndIndex",
+        ["withdrawalGroupId", "coinIdx"],
+        {
+          unique: true,
+        },
+      ),
       byGroup: describeIndex("byGroup", "withdrawalGroupId"),
       byCoinEvHash: describeIndex("byCoinEv", "coinEvHash"),
     },