diff --git a/.changeset/strange-fans-move.md b/.changeset/strange-fans-move.md
new file mode 100644
index 0000000000..a6b11da73a
--- /dev/null
+++ b/.changeset/strange-fans-move.md
@@ -0,0 +1,5 @@
+---
+"viem": patch
+---
+
+Resolved issue where hex-like strings were incorrectly being lowercased in `signTypedData`.
diff --git a/src/actions/wallet/signTypedData.ts b/src/actions/wallet/signTypedData.ts
index 51e26e5093..439a39104b 100644
--- a/src/actions/wallet/signTypedData.ts
+++ b/src/actions/wallet/signTypedData.ts
@@ -18,12 +18,13 @@ import type { Chain } from '../../types/chain.js'
 import type { Hex } from '../../types/misc.js'
 import type { TypedDataDefinition } from '../../types/typedData.js'
 import type { RequestErrorType } from '../../utils/buildRequest.js'
-import { type IsHexErrorType, isHex } from '../../utils/data/isHex.js'
-import { type StringifyErrorType, stringify } from '../../utils/stringify.js'
+import type { IsHexErrorType } from '../../utils/data/isHex.js'
+import type { StringifyErrorType } from '../../utils/stringify.js'
 import {
   type GetTypesForEIP712DomainErrorType,
   type ValidateTypedDataErrorType,
   getTypesForEIP712Domain,
+  serializeTypedData,
   validateTypedData,
 } from '../../utils/typedData.js'
 
@@ -181,10 +182,7 @@ export async function signTypedData<
   if (account.type === 'local')
     return account.signTypedData({ domain, message, primaryType, types })
 
-  const typedData = stringify(
-    { domain: domain ?? {}, message, primaryType, types },
-    (_, value) => (isHex(value) ? value.toLowerCase() : value),
-  )
+  const typedData = serializeTypedData({ domain, message, primaryType, types })
   return client.request(
     {
       method: 'eth_signTypedData_v4',
diff --git a/src/utils/typedData.test.ts b/src/utils/typedData.test.ts
index 59ce66e4f0..f0db83dd28 100644
--- a/src/utils/typedData.test.ts
+++ b/src/utils/typedData.test.ts
@@ -1,7 +1,136 @@
 import { describe, expect, test } from 'vitest'
 
 import { pad, toHex } from './index.js'
-import { domainSeparator, validateTypedData } from './typedData.js'
+import {
+  domainSeparator,
+  serializeTypedData,
+  validateTypedData,
+} from './typedData.js'
+
+describe('serializeTypedData', () => {
+  test('default', () => {
+    expect(
+      serializeTypedData({
+        domain: {
+          name: 'Ether!',
+          version: '1',
+          chainId: 1,
+          verifyingContract: '0xCcCCccccCCCCcCCCCCCcCcCccCcCCCcCcccccccC',
+        },
+        primaryType: 'Foo',
+        types: {
+          Foo: [
+            { name: 'address', type: 'address' },
+            { name: 'name', type: 'string' },
+            { name: 'foo', type: 'string' },
+          ],
+        },
+        message: {
+          address: '0xb9CAB4F0E46F7F6b1024b5A7463734fa68E633f9',
+          name: 'jxom',
+          foo: '0xb9CAB4F0E46F7F6b1024b5A7463734fa68E633f9',
+        },
+      }),
+    ).toMatchInlineSnapshot(
+      `"{"domain":{},"message":{"address":"0xb9cab4f0e46f7f6b1024b5a7463734fa68e633f9","name":"jxom","foo":"0xb9CAB4F0E46F7F6b1024b5A7463734fa68E633f9"},"primaryType":"Foo","types":{"Foo":[{"name":"address","type":"address"},{"name":"name","type":"string"},{"name":"foo","type":"string"}]}}"`,
+    )
+  })
+
+  test('with domain', () => {
+    expect(
+      serializeTypedData({
+        domain: {
+          name: 'Ether!',
+          version: '1',
+          address: '0xb9CAB4F0E46F7F6b1024b5A7463734fa68E633f9',
+          chainId: 1,
+          verifyingContract: '0xCcCCccccCCCCcCCCCCCcCcCccCcCCCcCcccccccC',
+        },
+        primaryType: 'Foo',
+        types: {
+          EIP712Domain: [
+            { name: 'name', type: 'string' },
+            { name: 'version', type: 'string' },
+            { name: 'address', type: 'address' },
+            { name: 'chainId', type: 'uint32' },
+            { name: 'verifyingContract', type: 'address' },
+          ],
+          Foo: [
+            { name: 'address', type: 'address' },
+            { name: 'name', type: 'string' },
+            { name: 'foo', type: 'string' },
+          ],
+        },
+        message: {
+          address: '0xb9CAB4F0E46F7F6b1024b5A7463734fa68E633f9',
+          name: 'jxom',
+          foo: '0xb9CAB4F0E46F7F6b1024b5A7463734fa68E633f9',
+        },
+      }),
+    ).toMatchInlineSnapshot(
+      `"{"domain":{"name":"Ether!","version":"1","address":"0xb9cab4f0e46f7f6b1024b5a7463734fa68e633f9","chainId":1,"verifyingContract":"0xcccccccccccccccccccccccccccccccccccccccc"},"message":{"address":"0xb9cab4f0e46f7f6b1024b5a7463734fa68e633f9","name":"jxom","foo":"0xb9CAB4F0E46F7F6b1024b5A7463734fa68E633f9"},"primaryType":"Foo","types":{"EIP712Domain":[{"name":"name","type":"string"},{"name":"version","type":"string"},{"name":"address","type":"address"},{"name":"chainId","type":"uint32"},{"name":"verifyingContract","type":"address"}],"Foo":[{"name":"address","type":"address"},{"name":"name","type":"string"},{"name":"foo","type":"string"}]}}"`,
+    )
+  })
+
+  test('domain as primary type', () => {
+    expect(
+      serializeTypedData({
+        domain: {
+          name: 'Ether!',
+          version: '1',
+          address: '0xb9CAB4F0E46F7F6b1024b5A7463734fa68E633f9',
+          chainId: 1,
+          verifyingContract: '0xCcCCccccCCCCcCCCCCCcCcCccCcCCCcCcccccccC',
+        },
+        primaryType: 'EIP712Domain',
+        types: {
+          EIP712Domain: [
+            { name: 'name', type: 'string' },
+            { name: 'version', type: 'string' },
+            { name: 'address', type: 'address' },
+            { name: 'chainId', type: 'uint32' },
+            { name: 'verifyingContract', type: 'address' },
+          ],
+          Foo: [
+            { name: 'address', type: 'address' },
+            { name: 'name', type: 'string' },
+            { name: 'foo', type: 'string' },
+          ],
+        },
+      }),
+    ).toMatchInlineSnapshot(
+      `"{"domain":{"name":"Ether!","version":"1","address":"0xb9cab4f0e46f7f6b1024b5a7463734fa68e633f9","chainId":1,"verifyingContract":"0xcccccccccccccccccccccccccccccccccccccccc"},"primaryType":"EIP712Domain","types":{"EIP712Domain":[{"name":"name","type":"string"},{"name":"version","type":"string"},{"name":"address","type":"address"},{"name":"chainId","type":"uint32"},{"name":"verifyingContract","type":"address"}],"Foo":[{"name":"address","type":"address"},{"name":"name","type":"string"},{"name":"foo","type":"string"}]}}"`,
+    )
+  })
+
+  test('no domain', () => {
+    expect(
+      serializeTypedData({
+        primaryType: 'Foo',
+        types: {
+          EIP712Domain: [
+            { name: 'name', type: 'string' },
+            { name: 'version', type: 'string' },
+            { name: 'chainId', type: 'uint32' },
+            { name: 'verifyingContract', type: 'address' },
+          ],
+          Foo: [
+            { name: 'address', type: 'address' },
+            { name: 'name', type: 'string' },
+            { name: 'foo', type: 'string' },
+          ],
+        },
+        message: {
+          address: '0xb9CAB4F0E46F7F6b1024b5A7463734fa68E633f9',
+          name: 'jxom',
+          foo: '0xb9CAB4F0E46F7F6b1024b5A7463734fa68E633f9',
+        },
+      }),
+    ).toMatchInlineSnapshot(
+      `"{"domain":{},"message":{"address":"0xb9cab4f0e46f7f6b1024b5a7463734fa68e633f9","name":"jxom","foo":"0xb9CAB4F0E46F7F6b1024b5A7463734fa68E633f9"},"primaryType":"Foo","types":{"EIP712Domain":[{"name":"name","type":"string"},{"name":"version","type":"string"},{"name":"chainId","type":"uint32"},{"name":"verifyingContract","type":"address"}],"Foo":[{"name":"address","type":"address"},{"name":"name","type":"string"},{"name":"foo","type":"string"}]}}"`,
+    )
+  })
+})
 
 describe('validateTypedData', () => {
   test('default', () => {
diff --git a/src/utils/typedData.ts b/src/utils/typedData.ts
index a3f0dc26e9..b934e9ec0b 100644
--- a/src/utils/typedData.ts
+++ b/src/utils/typedData.ts
@@ -14,6 +14,53 @@ import {
   type HashDomainErrorType,
   hashDomain,
 } from './signature/hashTypedData.js'
+import { stringify } from './stringify.js'
+
+export type SerializeTypedDataErrorType =
+  | HashDomainErrorType
+  | IsAddressErrorType
+  | NumberToHexErrorType
+  | SizeErrorType
+  | ErrorType
+
+export function serializeTypedData<
+  const typedData extends TypedData | Record<string, unknown>,
+  primaryType extends keyof typedData | 'EIP712Domain',
+>(parameters: TypedDataDefinition<typedData, primaryType>) {
+  const {
+    domain: domain_,
+    message: message_,
+    primaryType,
+    types,
+  } = parameters as unknown as TypedDataDefinition
+
+  const normalizeData = (
+    struct: readonly TypedDataParameter[],
+    data_: Record<string, unknown>,
+  ) => {
+    const data = { ...data_ }
+    for (const param of struct) {
+      const { name, type } = param
+      if (type === 'address') data[name] = (data[name] as string).toLowerCase()
+    }
+    return data
+  }
+
+  const domain = (() => {
+    if (!types.EIP712Domain) return {}
+    if (!domain_) return {}
+    return normalizeData(types.EIP712Domain, domain_)
+  })()
+
+  const message = (() => {
+    if (primaryType === 'EIP712Domain') return undefined
+    return normalizeData(types[primaryType], message_)
+  })()
+
+  console.log(message)
+
+  return stringify({ domain, message, primaryType, types })
+}
 
 export type ValidateTypedDataErrorType =
   | HashDomainErrorType
@@ -72,11 +119,8 @@ export function validateTypedData<
   // Validate domain types.
   if (types.EIP712Domain && domain) validateData(types.EIP712Domain, domain)
 
-  if (primaryType !== 'EIP712Domain') {
-    // Validate message types.
-    const type = types[primaryType]
-    validateData(type, message)
-  }
+  // Validate message types.
+  if (primaryType !== 'EIP712Domain') validateData(types[primaryType], message)
 }
 
 export type GetTypesForEIP712DomainErrorType = ErrorType