diff --git a/yarn-project/archiver/src/store/contract_class_store.test.ts b/yarn-project/archiver/src/store/contract_class_store.test.ts
index 42a389c84031..dd90be2e91a4 100644
--- a/yarn-project/archiver/src/store/contract_class_store.test.ts
+++ b/yarn-project/archiver/src/store/contract_class_store.test.ts
@@ -43,10 +43,13 @@ describe('ContractClassStore', () => {
       await expect(contractClassStore.getContractClass(contractClass.id)).resolves.toBeUndefined();
     });
 
-    it('throws if the same contract class is added again', async () => {
+    it('is a no-op if the same contract class is added again at a later block', async () => {
       await expect(
         contractClassStore.addContractClasses([await withCommitment(contractClass)], BlockNumber(blockNum + 1)),
-      ).rejects.toThrow(/already exists/);
+      ).resolves.toBe(true);
+      // Original l2BlockNumber is preserved, so a later delete at blockNum + 1 should not remove it.
+      await contractClassStore.deleteContractClasses([contractClass], BlockNumber(blockNum + 1));
+      await expect(contractClassStore.getContractClass(contractClass.id)).resolves.toMatchObject(contractClass);
     });
 
     it('returns contract class if deleted at a later block number', async () => {
diff --git a/yarn-project/archiver/src/store/contract_class_store.ts b/yarn-project/archiver/src/store/contract_class_store.ts
index ea3b5a48ef56..6e0c98996c04 100644
--- a/yarn-project/archiver/src/store/contract_class_store.ts
+++ b/yarn-project/archiver/src/store/contract_class_store.ts
@@ -49,14 +49,14 @@ export class ContractClassStore {
   ): Promise<void> {
     await this.db.transactionAsync(async () => {
       const key = contractClass.id.toString();
-      if (await this.#contractClasses.hasAsync(key)) {
-        throw new Error(`Contract class ${key} already exists, cannot add again at block ${blockNumber}`);
-      }
-      await this.#contractClasses.set(
+      // Class id is content-derived (artifactHash, privateFunctionsRoot, publicBytecodeCommitment),
+      // so a duplicate add carries identical data. Keep the original entry's l2BlockNumber so that
+      // a later rollback at a higher block leaves the class registered at its earliest block.
+      await this.#contractClasses.setIfNotExists(
         key,
         serializeContractClassPublic({ ...contractClass, l2BlockNumber: blockNumber }),
       );
-      await this.#bytecodeCommitments.set(key, bytecodeCommitment.toBuffer());
+      await this.#bytecodeCommitments.setIfNotExists(key, bytecodeCommitment.toBuffer());
     });
   }
 
diff --git a/yarn-project/archiver/src/store/contract_instance_store.test.ts b/yarn-project/archiver/src/store/contract_instance_store.test.ts
index f6330c2ed0a2..a58a866813f4 100644
--- a/yarn-project/archiver/src/store/contract_instance_store.test.ts
+++ b/yarn-project/archiver/src/store/contract_instance_store.test.ts
@@ -48,10 +48,11 @@ describe('ContractInstanceStore', () => {
       ).resolves.toBeUndefined();
     });
 
-    it('throws when adding the same contract instance twice', async () => {
-      await expect(contractInstanceStore.addContractInstances([contractInstance], BlockNumber(2))).rejects.toThrow(
-        /already exists/,
-      );
+    it('is a no-op when adding the same contract instance twice', async () => {
+      await expect(contractInstanceStore.addContractInstances([contractInstance], BlockNumber(2))).resolves.toBe(true);
+      await expect(
+        contractInstanceStore.getContractInstance(contractInstance.address, timestamp),
+      ).resolves.toMatchObject(contractInstance);
     });
   });
 
diff --git a/yarn-project/archiver/src/store/contract_instance_store.ts b/yarn-project/archiver/src/store/contract_instance_store.ts
index eed2aa55b681..7cd62fbb4749 100644
--- a/yarn-project/archiver/src/store/contract_instance_store.ts
+++ b/yarn-project/archiver/src/store/contract_instance_store.ts
@@ -71,13 +71,16 @@ export class ContractInstanceStore {
   addContractInstance(contractInstance: ContractInstanceWithAddress, blockNumber: number): Promise<void> {
     return this.db.transactionAsync(async () => {
       const key = contractInstance.address.toString();
-      if (await this.#contractInstances.hasAsync(key)) {
-        throw new Error(
-          `Contract instance at ${key} already exists (deployed at block ${await this.#contractInstancePublishedAt.getAsync(key)}), cannot add again at block ${blockNumber}`,
-        );
+      // Instance address is content-derived from instance fields, so a duplicate add carries
+      // identical data. Keep the original entry's blockNumber so that a later rollback at a higher
+      // block leaves the instance registered at its earliest block.
+      const inserted = await this.#contractInstances.setIfNotExists(
+        key,
+        new SerializableContractInstance(contractInstance).toBuffer(),
+      );
+      if (inserted) {
+        await this.#contractInstancePublishedAt.set(key, blockNumber);
       }
-      await this.#contractInstances.set(key, new SerializableContractInstance(contractInstance).toBuffer());
-      await this.#contractInstancePublishedAt.set(key, blockNumber);
     });
   }