diff --git a/packages/sdk/src/common/chains/unichain-sepolia.ts b/packages/sdk/src/common/chains/unichain-sepolia.ts
new file mode 100644
index 0000000..cd1bc5e
--- /dev/null
+++ b/packages/sdk/src/common/chains/unichain-sepolia.ts
@@ -0,0 +1,58 @@
+import { defineChain } from 'viem';
+import { chainConfig } from 'viem/op-stack';
+
+// TODO: replace with import from 'viem/chains'
+// Copy-pasted from
+// https://github.com/wevm/viem/blob/c52c8ed2a2e18d1e0d433fe87990bc5539d579be/src/chains/definitions/unichainSepolia.ts
+// Reason: we had to downgrade viem to 2.22.23 because of the critical issue with Safe
+// But viem v2.22.23 doesn't have Unichain support, so Unichain is defined here.
+// viem v2.23.1 added Unichain support
+
+const sourceId = 11_155_111; // sepolia
+
+export const unichainSepolia = defineChain({
+  ...chainConfig,
+  id: 1301,
+  name: 'Unichain Sepolia',
+  nativeCurrency: {
+    name: 'Ether',
+    symbol: 'ETH',
+    decimals: 18,
+  },
+  rpcUrls: {
+    default: {
+      http: ['https://sepolia.unichain.org'],
+    },
+  },
+  blockExplorers: {
+    default: {
+      name: 'Uniscan',
+      url: 'https://sepolia.uniscan.xyz',
+      apiUrl: 'https://api-sepolia.uniscan.xyz/api',
+    },
+  },
+  contracts: {
+    ...chainConfig.contracts,
+    multicall3: {
+      address: '0xca11bde05977b3631167028862be2a173976ca11',
+      blockCreated: 0,
+    },
+    portal: {
+      [sourceId]: {
+        address: '0x0d83dab629f0e0F9d36c0Cbc89B69a489f0751bD',
+      },
+    },
+    l1StandardBridge: {
+      [sourceId]: {
+        address: '0xea58fcA6849d79EAd1f26608855c2D6407d54Ce2',
+      },
+    },
+    disputeGameFactory: {
+      [sourceId]: {
+        address: '0xeff73e5aa3B9AEC32c659Aa3E00444d20a84394b',
+      },
+    },
+  },
+  testnet: true,
+  sourceId,
+});
diff --git a/packages/sdk/src/common/chains/unichain.ts b/packages/sdk/src/common/chains/unichain.ts
new file mode 100644
index 0000000..55c3c4f
--- /dev/null
+++ b/packages/sdk/src/common/chains/unichain.ts
@@ -0,0 +1,53 @@
+import { defineChain } from 'viem';
+import { chainConfig } from 'viem/op-stack';
+
+// TODO: replace with import from 'viem/chains'
+// Copy-pasted from
+// https://github.com/wevm/viem/blob/c52c8ed2a2e18d1e0d433fe87990bc5539d579be/src/chains/definitions/unichain.ts
+// Reason: we had to downgrade viem to 2.22.23 because of the critical issue with Safe
+// But viem v2.22.23 doesn't have Unichain support, so Unichain is defined here.
+// viem v2.23.1 added Unichain support
+
+const sourceId = 1; // mainnet
+
+export const unichain = defineChain({
+  ...chainConfig,
+  id: 130,
+  name: 'Unichain',
+  nativeCurrency: { name: 'Ether', symbol: 'ETH', decimals: 18 },
+  rpcUrls: {
+    default: {
+      http: ['https://mainnet.unichain.org/'],
+    },
+  },
+  blockExplorers: {
+    default: {
+      name: 'Uniscan',
+      url: 'https://uniscan.xyz',
+      apiUrl: 'https://api.uniscan.xyz/api',
+    },
+  },
+  contracts: {
+    ...chainConfig.contracts,
+    multicall3: {
+      address: '0xca11bde05977b3631167028862be2a173976ca11',
+      blockCreated: 0,
+    },
+    disputeGameFactory: {
+      [sourceId]: {
+        address: '0x2F12d621a16e2d3285929C9996f478508951dFe4',
+      },
+    },
+    portal: {
+      [sourceId]: {
+        address: '0x0bd48f6B86a26D3a217d0Fa6FfE2B491B956A7a2',
+      },
+    },
+    l1StandardBridge: {
+      [sourceId]: {
+        address: '0x81014F44b0a345033bB2b3B21C7a1A308B35fEeA',
+      },
+    },
+  },
+  sourceId,
+});
diff --git a/packages/sdk/src/common/constants.ts b/packages/sdk/src/common/constants.ts
index 9fa79db..c73b31b 100644
--- a/packages/sdk/src/common/constants.ts
+++ b/packages/sdk/src/common/constants.ts
@@ -7,9 +7,9 @@ import {
   optimism,
   soneiumMinato,
   soneium,
-  unichain,
-  unichainSepolia,
 } from 'viem/chains';
+import { unichain } from './chains/unichain.js';
+import { unichainSepolia } from './chains/unichain-sepolia.js';
 
 export enum CHAINS {
   Mainnet = 1,