diff --git a/contracts/imports/constants.fc b/contracts/imports/constants.fc
index 8491233..c260f95 100644
--- a/contracts/imports/constants.fc
+++ b/contracts/imports/constants.fc
@@ -5,9 +5,9 @@ int op::withdraw() asm "0x41836980 PUSHINT";
 int op::transfer_ownership() asm "0x2da38aaf PUSHINT";
 
 ;; errors
-int error::access_denied() asm "0xfffffffe PUSHINT";
-int error::unknown_op() asm "0xffffffff PUSHINT";
-int error::insufficient_balance() asm "101 PUSHINT";
+int error::unknown_op() asm "101 PUSHINT";
+int error::access_denied() asm "102 PUSHINT";
+int error::insufficient_balance() asm "103 PUSHINT";
 
 ;; other
 int const::min_tons_for_storage() asm "10000000 PUSHINT"; ;; 0.01 TON
\ No newline at end of file
diff --git a/contracts/main.ts b/contracts/main.ts
index 6410c3e..4d63119 100644
--- a/contracts/main.ts
+++ b/contracts/main.ts
@@ -5,8 +5,12 @@ export function data(params: { ownerAddress: Address; counter: number }): Cell {
   return beginCell().storeAddress(params.ownerAddress).storeUint(params.counter, 64).endCell();
 }
 
-// message encoders for all ops
+// message encoders for all ops (see contracts/imports/constants.fc for consts)
 
 export function increment(): Cell {
   return beginCell().storeUint(0x37491f2f, 32).storeUint(0, 64).endCell();
 }
+
+export function transferOwnership(params: { newOwnerAddress: Address }): Cell {
+  return beginCell().storeUint(0x2da38aaf, 32).storeUint(0, 64).storeAddress(params.newOwnerAddress).endCell();
+}
diff --git a/test/ownership.spec.ts b/test/ownership.spec.ts
new file mode 100644
index 0000000..7feac58
--- /dev/null
+++ b/test/ownership.spec.ts
@@ -0,0 +1,53 @@
+import chai, { expect } from "chai";
+import chaiBN from "chai-bn";
+import BN from "bn.js";
+chai.use(chaiBN(BN));
+
+import * as fs from "fs";
+import { Cell, Slice } from "ton";
+import { SmartContract } from "ton-contract-executor";
+import * as main from "../contracts/main";
+import { internalMessage, randomAddress } from "./helpers";
+
+describe("Transfer ownership tests", () => {
+  let contract: SmartContract;
+
+  beforeEach(async () => {
+    contract = await SmartContract.fromCell(
+      Cell.fromBoc(fs.readFileSync("build/main.cell"))[0], // code cell from build output
+      main.data({
+        ownerAddress: randomAddress("owner"),
+        counter: 17,
+      })
+    );
+  });
+
+  it("should allow the owner to change owners", async () => {
+    const send = await contract.sendInternalMessage(
+      internalMessage({
+        from: randomAddress("owner"),
+        body: main.transferOwnership({ newOwnerAddress: randomAddress("newowner") }),
+      })
+    );
+    expect(send.type).to.equal("success");
+
+    const call = await contract.invokeGetMethod("owner_address", []);
+    const address = (call.result[0] as Slice).readAddress();
+    expect(address?.equals(randomAddress("newowner"))).to.equal(true);
+  });
+
+  it("should prevent others from changing owners", async () => {
+    const send = await contract.sendInternalMessage(
+      internalMessage({
+        from: randomAddress("notowner"),
+        body: main.transferOwnership({ newOwnerAddress: randomAddress("newowner") }),
+      })
+    );
+    expect(send.type).to.equal("failed");
+    expect(send.exit_code).to.equal(102); // access_denied in contracts/imports/constants.fc
+
+    const call = await contract.invokeGetMethod("owner_address", []);
+    const address = (call.result[0] as Slice).readAddress();
+    expect(address?.equals(randomAddress("owner"))).to.equal(true);
+  });
+});