diff --git a/packages/taler-wallet-core/src/operations/common.ts b/packages/taler-wallet-core/src/operations/common.ts
index d75869043..f6572c851 100644
--- a/packages/taler-wallet-core/src/operations/common.ts
+++ b/packages/taler-wallet-core/src/operations/common.ts
@@ -467,11 +467,11 @@ export type ParsedTombstone =
     }
   | { tag: TombstoneTag.DeleteRefund; refundGroupId: string };
 
-export function constructTombstone(p: ParsedTombstone): string {
+export function constructTombstone(p: ParsedTombstone): TombstoneIdStr {
   switch (p.tag) {
     case TombstoneTag.DeleteWithdrawalGroup:
-      return `tmb:${p.tag}:${p.withdrawalGroupId}`;
+      return `tmb:${p.tag}:${p.withdrawalGroupId}` as TombstoneIdStr;
     case TombstoneTag.DeleteRefund:
-      return `tmb:${p.tag}:${p.refundGroupId}`;
+      return `tmb:${p.tag}:${p.refundGroupId}` as TombstoneIdStr;
   }
 }