diff --git a/yarn-project/aztec-node/src/aztec-node/server.ts b/yarn-project/aztec-node/src/aztec-node/server.ts
index cc851ee4258..8ba10d55298 100644
--- a/yarn-project/aztec-node/src/aztec-node/server.ts
+++ b/yarn-project/aztec-node/src/aztec-node/server.ts
@@ -327,7 +327,7 @@ export class AztecNodeService implements AztecNode {
    * @returns The index of the given leaf in the given tree or undefined if not found.
    */
   public async findLeafIndex(
-    blockNumber: number | 'latest',
+    blockNumber: BlockNumber,
     treeId: MerkleTreeId,
     leafValue: Fr,
   ): Promise<bigint | undefined> {
@@ -342,7 +342,7 @@ export class AztecNodeService implements AztecNode {
    * @returns The sibling path for the leaf index.
    */
   public async getNullifierSiblingPath(
-    blockNumber: number | 'latest',
+    blockNumber: BlockNumber,
     leafIndex: bigint,
   ): Promise<SiblingPath<typeof NULLIFIER_TREE_HEIGHT>> {
     const committedDb = await this.#getWorldState(blockNumber);
@@ -356,7 +356,7 @@ export class AztecNodeService implements AztecNode {
    * @returns The sibling path for the leaf index.
    */
   public async getNoteHashSiblingPath(
-    blockNumber: number | 'latest',
+    blockNumber: BlockNumber,
     leafIndex: bigint,
   ): Promise<SiblingPath<typeof NOTE_HASH_TREE_HEIGHT>> {
     const committedDb = await this.#getWorldState(blockNumber);
@@ -393,7 +393,7 @@ export class AztecNodeService implements AztecNode {
    * @returns A tuple of the index and the sibling path of the L2ToL1Message.
    */
   public async getL2ToL1MessageIndexAndSiblingPath(
-    blockNumber: number | 'latest',
+    blockNumber: BlockNumber,
     l2ToL1Message: Fr,
   ): Promise<[number, SiblingPath<number>]> {
     const block = await this.blockSource.getBlock(blockNumber === 'latest' ? await this.getBlockNumber() : blockNumber);
@@ -431,7 +431,7 @@ export class AztecNodeService implements AztecNode {
    * @returns The sibling path.
    */
   public async getArchiveSiblingPath(
-    blockNumber: number | 'latest',
+    blockNumber: BlockNumber,
     leafIndex: bigint,
   ): Promise<SiblingPath<typeof ARCHIVE_HEIGHT>> {
     const committedDb = await this.#getWorldState(blockNumber);
@@ -445,7 +445,7 @@ export class AztecNodeService implements AztecNode {
    * @returns The sibling path.
    */
   public async getPublicDataSiblingPath(
-    blockNumber: number | 'latest',
+    blockNumber: BlockNumber,
     leafIndex: bigint,
   ): Promise<SiblingPath<typeof PUBLIC_DATA_TREE_HEIGHT>> {
     const committedDb = await this.#getWorldState(blockNumber);
@@ -459,7 +459,7 @@ export class AztecNodeService implements AztecNode {
    * @returns The nullifier membership witness (if found).
    */
   public async getNullifierMembershipWitness(
-    blockNumber: number | 'latest',
+    blockNumber: BlockNumber,
     nullifier: Fr,
   ): Promise<NullifierMembershipWitness | undefined> {
     const db = await this.#getWorldState(blockNumber);
@@ -498,7 +498,7 @@ export class AztecNodeService implements AztecNode {
    * TODO: This is a confusing behavior and we should eventually address that.
    */
   public async getLowNullifierMembershipWitness(
-    blockNumber: number | 'latest',
+    blockNumber: BlockNumber,
     nullifier: Fr,
   ): Promise<NullifierMembershipWitness | undefined> {
     const committedDb = await this.#getWorldState(blockNumber);
@@ -519,7 +519,7 @@ export class AztecNodeService implements AztecNode {
     return new NullifierMembershipWitness(BigInt(index), preimageData as NullifierLeafPreimage, siblingPath);
   }
 
-  async getPublicDataTreeWitness(blockNumber: number | 'latest', leafSlot: Fr): Promise<PublicDataWitness | undefined> {
+  async getPublicDataTreeWitness(blockNumber: BlockNumber, leafSlot: Fr): Promise<PublicDataWitness | undefined> {
     const committedDb = await this.#getWorldState(blockNumber);
     const lowLeafResult = await committedDb.getPreviousValueIndex(MerkleTreeId.PUBLIC_DATA_TREE, leafSlot.toBigInt());
     if (!lowLeafResult) {
@@ -631,7 +631,7 @@ export class AztecNodeService implements AztecNode {
    * @param blockNumber - The block number at which to get the data.
    * @returns An instance of a committed MerkleTreeOperations
    */
-  async #getWorldState(blockNumber: number | 'latest') {
+  async #getWorldState(blockNumber: BlockNumber) {
     if (typeof blockNumber === 'number' && blockNumber < INITIAL_L2_BLOCK_NUM) {
       throw new Error('Invalid block number to get world state for: ' + blockNumber);
     }
diff --git a/yarn-project/circuit-types/src/interfaces/aztec-node.ts b/yarn-project/circuit-types/src/interfaces/aztec-node.ts
index dffadd90541..2d25ab3a0b8 100644
--- a/yarn-project/circuit-types/src/interfaces/aztec-node.ts
+++ b/yarn-project/circuit-types/src/interfaces/aztec-node.ts
@@ -17,13 +17,11 @@ import { MerkleTreeId } from '../merkle_tree_id.js';
 import { SiblingPath } from '../sibling_path/index.js';
 import { Tx, TxHash, TxReceipt } from '../tx/index.js';
 import { TxEffect } from '../tx_effect.js';
+import { BlockNumber } from './block_number.js';
 import { SequencerConfig } from './configs.js';
 import { NullifierMembershipWitness } from './nullifier_tree.js';
 import { PublicDataWitness } from './public_data_tree.js';
 
-/** Helper type for a specific L2 block number or the latest block number */
-export type BlockNumber = number | 'latest';
-
 /**
  * The aztec node.
  * We will probably implement the additional interfaces by means other than Aztec Node as it's currently a privacy leak
diff --git a/yarn-project/circuit-types/src/interfaces/block_number.ts b/yarn-project/circuit-types/src/interfaces/block_number.ts
new file mode 100644
index 00000000000..aaf0c954d66
--- /dev/null
+++ b/yarn-project/circuit-types/src/interfaces/block_number.ts
@@ -0,0 +1,2 @@
+/** Helper type for a specific L2 block number or the latest block number */
+export type BlockNumber = number | 'latest';
diff --git a/yarn-project/circuit-types/src/interfaces/index.ts b/yarn-project/circuit-types/src/interfaces/index.ts
index f12dff9dfcd..9ec6483a806 100644
--- a/yarn-project/circuit-types/src/interfaces/index.ts
+++ b/yarn-project/circuit-types/src/interfaces/index.ts
@@ -1,4 +1,5 @@
 export * from './aztec-node.js';
+export * from './block_number.js';
 export * from './pxe.js';
 export * from './deployed-contract.js';
 export * from './sync-status.js';