diff --git a/packages/stacking/README.md b/packages/stacking/README.md
index 112d912fe..97f932c59 100644
--- a/packages/stacking/README.md
+++ b/packages/stacking/README.md
@@ -93,6 +93,8 @@ const amountMicroStx = 100000000000n;
 const privateKey = 'd48f215481c16cbe6426f8e557df9b78895661971d71735126545abddcd5377001';
 // block height at which to stack
 const burnBlockHeight = 2000;
+// signer key hex
+const signerKey = '03bae4a7...e2e2c6b7e';
 
 // Refer to initialization section to create client instance
 const stackingResults = await client.stack({
@@ -101,6 +103,7 @@ const stackingResults = await client.stack({
   cycles,
   privateKey,
   burnBlockHeight,
+  signerKey,
 });
 
 // {
diff --git a/packages/stacking/src/index.ts b/packages/stacking/src/index.ts
index 6ffb25db6..beef45e3f 100644
--- a/packages/stacking/src/index.ts
+++ b/packages/stacking/src/index.ts
@@ -1,5 +1,5 @@
 // @ts-ignore
-import { IntegerType, intToBigInt } from '@stacks/common';
+import { IntegerType, hexToBytes, intToBigInt } from '@stacks/common';
 import { StacksNetwork } from '@stacks/network';
 import {
   BurnchainRewardListResponse,
@@ -21,6 +21,7 @@ import {
   TxBroadcastResult,
   UIntCV,
   broadcastTransaction,
+  bufferCV,
   callReadOnlyFunction,
   cvToString,
   getFee,
@@ -36,6 +37,7 @@ import { PoxOperationPeriod, StackingErrors } from './constants';
 import {
   ensureLegacyBtcAddressForPox1,
   ensurePox2Activated,
+  ensureSignerKeyForPox4,
   poxAddressToTuple,
   unwrap,
   unwrapMap,
@@ -233,6 +235,8 @@ export interface LockStxOptions {
   amountMicroStx: IntegerType;
   /** the burnchain block height to begin lock */
   burnBlockHeight: number;
+  /** hex-encoded signer key `(buff 33)`, required for >= pox-4 */
+  signerKey?: string;
 }
 
 /**
@@ -661,6 +665,8 @@ export class StackingClient {
   }
 
   /**
+   * `stack-stx`
+   *
    * Generate and broadcast a stacking transaction to lock STX
    * @param {LockStxOptions} options - a required lock STX options object
    * @returns {Promise<string>} that resolves to a broadcasted txid if the operation succeeds
@@ -670,6 +676,7 @@ export class StackingClient {
     poxAddress,
     cycles,
     burnBlockHeight,
+    signerKey,
     ...txOptions
   }: LockStxOptions & BaseTxOptions): Promise<TxBroadcastResult> {
     const poxInfo = await this.getPoxInfo();
@@ -677,6 +684,7 @@ export class StackingClient {
 
     const contract = await this.getStackingContract(poxOperationInfo);
     ensureLegacyBtcAddressForPox1({ contract, poxAddress });
+    ensureSignerKeyForPox4({ contract, signerKey });
 
     const callOptions = this.getStackOptions({
       amountMicroStx,
@@ -684,6 +692,7 @@ export class StackingClient {
       poxAddress,
       contract,
       burnBlockHeight,
+      signerKey,
     });
     const tx = await makeContractCall({
       ...callOptions,
@@ -1006,21 +1015,31 @@ export class StackingClient {
     cycles,
     contract,
     burnBlockHeight,
+    signerKey,
   }: {
     cycles: number;
     poxAddress: string;
     amountMicroStx: IntegerType;
     contract: string;
     burnBlockHeight: number;
+    signerKey?: string;
   }) {
     const address = poxAddressToTuple(poxAddress);
     const [contractAddress, contractName] = this.parseContractId(contract);
+
+    const functionArgs = [
+      uintCV(amountMicroStx),
+      address,
+      uintCV(burnBlockHeight),
+      uintCV(cycles),
+    ] as ClarityValue[];
+    if (signerKey) functionArgs.push(bufferCV(hexToBytes(signerKey)));
+
     const callOptions: ContractCallOptions = {
       contractAddress,
       contractName,
       functionName: 'stack-stx',
-      // sum of uStx, address, burn_block_height, num_cycles
-      functionArgs: [uintCV(amountMicroStx), address, uintCV(burnBlockHeight), uintCV(cycles)],
+      functionArgs,
       validateWithAbi: true,
       network: this.network,
       anchorMode: AnchorMode.Any,
diff --git a/packages/stacking/src/utils.ts b/packages/stacking/src/utils.ts
index 3372dd681..c8fe5abc2 100644
--- a/packages/stacking/src/utils.ts
+++ b/packages/stacking/src/utils.ts
@@ -349,3 +349,19 @@ export function ensureLegacyBtcAddressForPox1({
     throw new Error('PoX-1 requires P2PKH/P2SH/P2SH-P2WPKH/P2SH-P2WSH bitcoin addresses');
   }
 }
+
+/**
+ * @internal
+ * Throws unless a signerKey is given for >= PoX-4.
+ */
+export function ensureSignerKeyForGtePox4({
+  contract,
+  signerKey,
+}: {
+  contract: string;
+  signerKey?: string;
+}) {
+  if (signerKey) return;
+  if (/\.pox(-[2-3])?$/.test(contract)) return;
+  throw new Error('PoX-4 requires a signer-key (buff 33) to stack');
+}