diff --git a/packages/identity/src/identity/delegation.test.ts b/packages/identity/src/identity/delegation.test.ts
index 8500778a4..f5bfd27a8 100644
--- a/packages/identity/src/identity/delegation.test.ts
+++ b/packages/identity/src/identity/delegation.test.ts
@@ -164,3 +164,29 @@ test('Delegation targets cannot exceed 1_000', () => {
     'Delegation targets cannot exceed 1000',
   );
 });
+
+test('Delegation chains cannot repeat public keys', async () => {
+  const root = createIdentity(0);
+  const middle = createIdentity(1);
+  const bottom = createIdentity(2);
+
+  const rootToMiddle = await DelegationChain.create(
+    root,
+    middle.getPublicKey(),
+    new Date(1609459200000),
+  );
+  const middleToBottom = await DelegationChain.create(
+    middle,
+    bottom.getPublicKey(),
+    new Date(1609459200000),
+    {
+      previous: rootToMiddle,
+    },
+  );
+
+  expect(
+    DelegationChain.create(bottom, root.getPublicKey(), new Date(1609459200000), {
+      previous: middleToBottom,
+    }),
+  ).rejects.toThrow('Delegation chain cannot repeat public keys');
+});
diff --git a/packages/identity/src/identity/delegation.ts b/packages/identity/src/identity/delegation.ts
index 98db784bc..4339dc27c 100644
--- a/packages/identity/src/identity/delegation.ts
+++ b/packages/identity/src/identity/delegation.ts
@@ -195,6 +195,18 @@ export class DelegationChain {
       targets?: Principal[];
     } = {},
   ): Promise<DelegationChain> {
+    if (options.previous) {
+      const delegatedKeys: PublicKey[] = [
+        ...options.previous.delegations.map(signedDelegation => signedDelegation.delegation.pubkey),
+        from.getPublicKey(),
+        to,
+      ];
+      const delegatedKeysSet = new Set(delegatedKeys.map(key => toHexString(key.derKey)));
+      if (delegatedKeys.length !== delegatedKeysSet.size) {
+        throw new DelegationError('Delegation chain cannot repeat public keys');
+      }
+    }
+
     const delegation = await _createSingleDelegation(from, to, expiration, options.targets);
     return new DelegationChain(
       [...(options.previous?.delegations || []), delegation],
@@ -255,6 +267,7 @@ export class DelegationChain {
   protected constructor(
     public readonly delegations: SignedDelegation[],
     public readonly publicKey: DerEncodedPublicKey,
+    public readonly previous?: DelegationChain,
   ) {
     if (delegations.length > MAXIMUM_DELEGATION_CHAIN_LENGTH) {
       throw new DelegationError(