diff --git a/.changeset/fair-lemons-retire.md b/.changeset/fair-lemons-retire.md
new file mode 100644
index 0000000000..f77f94798d
--- /dev/null
+++ b/.changeset/fair-lemons-retire.md
@@ -0,0 +1,5 @@
+---
+"viem": patch
+---
+
+Fixed legacy EIP-155 transaction serializing.
diff --git a/src/utils/transaction/serializeTransaction.test.ts b/src/utils/transaction/serializeTransaction.test.ts
index 810611d80a..2211fd8f43 100644
--- a/src/utils/transaction/serializeTransaction.test.ts
+++ b/src/utils/transaction/serializeTransaction.test.ts
@@ -615,3 +615,135 @@ test('cannot infer type from transaction object', () => {
     Version: viem@1.0.2"
   `)
 })
+
+describe('github', () => {
+  test('https://github.com/wagmi-dev/viem/issues/1433', () => {
+    expect(
+      serializeTransaction(
+        {
+          blockHash: null,
+          blockNumber: null,
+          from: '0xc702b9950e44f7d321fa16ee88bf8e1a561249ba',
+          gas: 51627n,
+          gasPrice: 3000000000n,
+          hash: '0x3eaa88a766e82cbe53c95218ab4c3cf316325802b5f75d086b5121007b918e92',
+          input:
+            '0xa9059cbb00000000000000000000000082fc882199816bcec06baf848eaec51c2f96c85b000000000000000000000000000000000000000000000000eccae3078bacd15d',
+          nonce: 117,
+          to: '0x55d398326f99059ff775485246999027b3197955',
+          transactionIndex: null,
+          value: 0n,
+          type: 'legacy',
+          v: 84475n,
+          r: '0x73b39769ff4a36515c8fca546550a3fdafebbf37fa9e22be2d92b44653ade7bf',
+          s: '0x354c756a1aa3346e9b3ea5423ac99acfc005e9cce2cd698e14d792f43fa15a23',
+          chainId: undefined,
+          typeHex: '0x0',
+        },
+        {
+          v: 84475n,
+          r: '0x73b39769ff4a36515c8fca546550a3fdafebbf37fa9e22be2d92b44653ade7bf',
+          s: '0x354c756a1aa3346e9b3ea5423ac99acfc005e9cce2cd698e14d792f43fa15a23',
+        },
+      ),
+    ).toMatchInlineSnapshot(
+      '"0xf8667584b2d05e0082c9ab9455d398326f99059ff775485246999027b31979558080830149fba073b39769ff4a36515c8fca546550a3fdafebbf37fa9e22be2d92b44653ade7bfa0354c756a1aa3346e9b3ea5423ac99acfc005e9cce2cd698e14d792f43fa15a23"',
+    )
+
+    expect(
+      serializeTransaction(
+        {
+          blockHash: null,
+          blockNumber: null,
+          from: '0xc702b9950e44f7d321fa16ee88bf8e1a561249ba',
+          gas: 51627n,
+          gasPrice: 3000000000n,
+          hash: '0x3eaa88a766e82cbe53c95218ab4c3cf316325802b5f75d086b5121007b918e92',
+          input:
+            '0xa9059cbb00000000000000000000000082fc882199816bcec06baf848eaec51c2f96c85b000000000000000000000000000000000000000000000000eccae3078bacd15d',
+          nonce: 117,
+          to: '0x55d398326f99059ff775485246999027b3197955',
+          transactionIndex: null,
+          value: 0n,
+          type: 'legacy',
+          v: 84476n,
+          r: '0x73b39769ff4a36515c8fca546550a3fdafebbf37fa9e22be2d92b44653ade7bf',
+          s: '0x354c756a1aa3346e9b3ea5423ac99acfc005e9cce2cd698e14d792f43fa15a23',
+          chainId: undefined,
+          typeHex: '0x0',
+        },
+        {
+          v: 84476n,
+          r: '0x73b39769ff4a36515c8fca546550a3fdafebbf37fa9e22be2d92b44653ade7bf',
+          s: '0x354c756a1aa3346e9b3ea5423ac99acfc005e9cce2cd698e14d792f43fa15a23',
+        },
+      ),
+    ).toMatchInlineSnapshot(
+      '"0xf8667584b2d05e0082c9ab9455d398326f99059ff775485246999027b31979558080830149fca073b39769ff4a36515c8fca546550a3fdafebbf37fa9e22be2d92b44653ade7bfa0354c756a1aa3346e9b3ea5423ac99acfc005e9cce2cd698e14d792f43fa15a23"',
+    )
+
+    expect(
+      serializeTransaction(
+        {
+          blockHash: null,
+          blockNumber: null,
+          from: '0xc702b9950e44f7d321fa16ee88bf8e1a561249ba',
+          gas: 51627n,
+          gasPrice: 3000000000n,
+          hash: '0x3eaa88a766e82cbe53c95218ab4c3cf316325802b5f75d086b5121007b918e92',
+          input:
+            '0xa9059cbb00000000000000000000000082fc882199816bcec06baf848eaec51c2f96c85b000000000000000000000000000000000000000000000000eccae3078bacd15d',
+          nonce: 117,
+          to: '0x55d398326f99059ff775485246999027b3197955',
+          transactionIndex: null,
+          value: 0n,
+          type: 'legacy',
+          v: 35n,
+          r: '0x73b39769ff4a36515c8fca546550a3fdafebbf37fa9e22be2d92b44653ade7bf',
+          s: '0x354c756a1aa3346e9b3ea5423ac99acfc005e9cce2cd698e14d792f43fa15a23',
+          chainId: undefined,
+          typeHex: '0x0',
+        },
+        {
+          v: 35n,
+          r: '0x73b39769ff4a36515c8fca546550a3fdafebbf37fa9e22be2d92b44653ade7bf',
+          s: '0x354c756a1aa3346e9b3ea5423ac99acfc005e9cce2cd698e14d792f43fa15a23',
+        },
+      ),
+    ).toMatchInlineSnapshot(
+      '"0xf8637584b2d05e0082c9ab9455d398326f99059ff775485246999027b319795580801ba073b39769ff4a36515c8fca546550a3fdafebbf37fa9e22be2d92b44653ade7bfa0354c756a1aa3346e9b3ea5423ac99acfc005e9cce2cd698e14d792f43fa15a23"',
+    )
+
+    expect(
+      serializeTransaction(
+        {
+          blockHash: null,
+          blockNumber: null,
+          from: '0xc702b9950e44f7d321fa16ee88bf8e1a561249ba',
+          gas: 51627n,
+          gasPrice: 3000000000n,
+          hash: '0x3eaa88a766e82cbe53c95218ab4c3cf316325802b5f75d086b5121007b918e92',
+          input:
+            '0xa9059cbb00000000000000000000000082fc882199816bcec06baf848eaec51c2f96c85b000000000000000000000000000000000000000000000000eccae3078bacd15d',
+          nonce: 117,
+          to: '0x55d398326f99059ff775485246999027b3197955',
+          transactionIndex: null,
+          value: 0n,
+          type: 'legacy',
+          v: 36n,
+          r: '0x73b39769ff4a36515c8fca546550a3fdafebbf37fa9e22be2d92b44653ade7bf',
+          s: '0x354c756a1aa3346e9b3ea5423ac99acfc005e9cce2cd698e14d792f43fa15a23',
+          chainId: undefined,
+          typeHex: '0x0',
+        },
+        {
+          v: 36n,
+          r: '0x73b39769ff4a36515c8fca546550a3fdafebbf37fa9e22be2d92b44653ade7bf',
+          s: '0x354c756a1aa3346e9b3ea5423ac99acfc005e9cce2cd698e14d792f43fa15a23',
+        },
+      ),
+    ).toMatchInlineSnapshot(
+      '"0xf8637584b2d05e0082c9ab9455d398326f99059ff775485246999027b319795580801ca073b39769ff4a36515c8fca546550a3fdafebbf37fa9e22be2d92b44653ade7bfa0354c756a1aa3346e9b3ea5423ac99acfc005e9cce2cd698e14d792f43fa15a23"',
+    )
+  })
+})
diff --git a/src/utils/transaction/serializeTransaction.ts b/src/utils/transaction/serializeTransaction.ts
index 82d0dd8b00..cc35067f2e 100644
--- a/src/utils/transaction/serializeTransaction.ts
+++ b/src/utils/transaction/serializeTransaction.ts
@@ -203,10 +203,23 @@ function serializeTransactionLegacy(
   ]
 
   if (signature) {
-    let v = 27n + (signature.v === 27n ? 0n : 1n)
-    if (chainId > 0) v = BigInt(chainId * 2) + BigInt(35n + signature.v - 27n)
-    else if (signature.v !== v)
-      throw new InvalidLegacyVError({ v: signature.v })
+    const v = (() => {
+      // EIP-155 (explicit chainId)
+      if (chainId > 0)
+        return BigInt(chainId * 2) + BigInt(35n + signature.v - 27n)
+
+      // EIP-155 (inferred chainId)
+      if (signature.v >= 35n) {
+        const inferredChainId = (signature.v - 35n) / 2n
+        if (inferredChainId > 0) return signature.v
+        return 27n + (signature.v === 35n ? 0n : 1n)
+      }
+
+      // Pre-EIP-155 (no chainId)
+      const v = 27n + (signature.v === 27n ? 0n : 1n)
+      if (signature.v !== v) throw new InvalidLegacyVError({ v: signature.v })
+      return v
+    })()
 
     serializedTransaction = [
       ...serializedTransaction,