diff --git a/.changeset/paymaster-context-presence.md b/.changeset/paymaster-context-presence.md
new file mode 100644
index 0000000000..bd90de2d55
--- /dev/null
+++ b/.changeset/paymaster-context-presence.md
@@ -0,0 +1,5 @@
+---
+"viem": patch
+---
+
+Fixed `prepareUserOperation` dropping a falsy per-operation `paymasterContext` (`false`, `0`, or `''`) in favor of the bundler client default.
diff --git a/src/account-abstraction/actions/bundler/prepareUserOperation.paymasterContext.test.ts b/src/account-abstraction/actions/bundler/prepareUserOperation.paymasterContext.test.ts
new file mode 100644
index 0000000000..cca1505c88
--- /dev/null
+++ b/src/account-abstraction/actions/bundler/prepareUserOperation.paymasterContext.test.ts
@@ -0,0 +1,148 @@
+import { createServer } from 'node:http'
+import { describe, expect, test } from 'vitest'
+import { mainnet } from '../../../chains/index.js'
+import { createClient } from '../../../clients/createClient.js'
+import { http } from '../../../clients/transports/http.js'
+import { stringToHex } from '../../../utils/encoding/toHex.js'
+import { toSmartAccount } from '../../accounts/toSmartAccount.js'
+import { createBundlerClient } from '../../clients/createBundlerClient.js'
+import { createPaymasterClient } from '../../clients/createPaymasterClient.js'
+import { prepareUserOperation } from './prepareUserOperation.js'
+
+const paymaster = '0x0000000000000000000000000000000000000001'
+
+async function setup() {
+  const server = createServer((req, res) => {
+    let data = ''
+    req.on('data', (chunk) => {
+      data += chunk
+    })
+    req.on('end', () => {
+      const { id, method, params } = JSON.parse(data)
+      if (
+        method !== 'pm_getPaymasterStubData' &&
+        method !== 'pm_getPaymasterData'
+      ) {
+        res.writeHead(200, { 'Content-Type': 'application/json' })
+        res.end(
+          JSON.stringify({
+            id,
+            jsonrpc: '2.0',
+            error: { code: -32601, message: 'Method not found' },
+          }),
+        )
+        return
+      }
+
+      const context = params[3]
+      res.writeHead(200, { 'Content-Type': 'application/json' })
+      res.end(
+        JSON.stringify({
+          id,
+          jsonrpc: '2.0',
+          result: {
+            paymaster,
+            paymasterData: stringToHex(JSON.stringify(context ?? null)),
+          },
+        }),
+      )
+    })
+  })
+  await new Promise<void>((resolve) => server.listen(0, resolve))
+  const address = server.address()
+  const port = typeof address === 'object' && address ? address.port : 0
+
+  const account = await toSmartAccount({
+    client: createClient({
+      chain: mainnet,
+      transport: http('http://localhost:1'),
+    }),
+    entryPoint: {
+      abi: [],
+      address: '0x0000000071727De22E5E9d8BAf0edAc6f37da032',
+      version: '0.7',
+    },
+    getAddress: async () => '0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266',
+    encodeCalls: async () => '0x',
+    getFactoryArgs: async () => ({}),
+    getStubSignature: async () => '0x',
+    signMessage: async () => '0x',
+    signTypedData: async () => '0x',
+    signUserOperation: async () => '0x',
+  })
+
+  const paymasterClient = createPaymasterClient({
+    transport: http(`http://localhost:${port}`),
+  })
+
+  return {
+    account,
+    bundlerClient: (paymasterContext: unknown) =>
+      createBundlerClient({
+        chain: mainnet,
+        paymaster: paymasterClient,
+        ...(paymasterContext !== undefined ? { paymasterContext } : {}),
+        transport: http('http://localhost:1'),
+      }),
+    close: () => new Promise<void>((resolve) => server.close(() => resolve())),
+  }
+}
+
+describe('paymasterContext', () => {
+  test.each([
+    { name: 'false', value: false },
+    { name: '0', value: 0 },
+    { name: "''", value: '' },
+    { name: 'object', value: { source: 'op' } },
+  ])(
+    'forwards a falsy per-operation paymasterContext ($name) instead of the client default',
+    async ({ value }) => {
+      const { account, bundlerClient, close } = await setup()
+
+      const request = await prepareUserOperation(
+        bundlerClient({ source: 'client-default' }),
+        {
+          account,
+          callData: '0x',
+          parameters: ['paymaster'] as const,
+          paymasterContext: value,
+        },
+      )
+      await close()
+
+      expect(request.paymasterData).toBe(stringToHex(JSON.stringify(value)))
+    },
+  )
+
+  test('falls back to the client default when no per-operation paymasterContext is given', async () => {
+    const { account, bundlerClient, close } = await setup()
+
+    const request = await prepareUserOperation(
+      bundlerClient({ source: 'client-default' }),
+      {
+        account,
+        callData: '0x',
+        parameters: ['paymaster'] as const,
+      },
+    )
+    await close()
+
+    expect(request.paymasterData).toBe(
+      stringToHex(JSON.stringify({ source: 'client-default' })),
+    )
+  })
+
+  test('forwards a falsy per-operation paymasterContext when no client default exists', async () => {
+    const { account, bundlerClient, close } = await setup()
+
+    const request = await prepareUserOperation(bundlerClient(undefined), {
+      account,
+      callData: '0x',
+      parameters: ['paymaster'] as const,
+      paymasterContext: false,
+    })
+    await close()
+
+    expect(request.paymasterData).toBe(stringToHex(JSON.stringify(false)))
+  })
+})
diff --git a/src/account-abstraction/actions/bundler/prepareUserOperation.ts b/src/account-abstraction/actions/bundler/prepareUserOperation.ts
index fc225cd7ea..cd2d69e47f 100644
--- a/src/account-abstraction/actions/bundler/prepareUserOperation.ts
+++ b/src/account-abstraction/actions/bundler/prepareUserOperation.ts
@@ -403,9 +403,10 @@ export async function prepareUserOperation<
       getPaymasterData: undefined,
     }
   })()
-  const paymasterContext = parameters.paymasterContext
-    ? parameters.paymasterContext
-    : bundlerClient?.paymasterContext
+  const paymasterContext =
+    parameters.paymasterContext !== undefined
+      ? parameters.paymasterContext
+      : bundlerClient?.paymasterContext
 
   ////////////////////////////////////////////////////////////////////////////////
   // Set up the User Operation request.