diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6936044..2f2e7df 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -8,3 +8,10 @@ jobs:
       - uses: actions/setup-node@v4
         with: {node-version: 20}
       - run: npm ci && npm run build
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with: {node-version: 20}
+      - run: npm ci && npm test
diff --git a/src/context/WalletContext.test.tsx b/src/context/WalletContext.test.tsx
index 5086977..8d75416 100644
--- a/src/context/WalletContext.test.tsx
+++ b/src/context/WalletContext.test.tsx
@@ -20,6 +20,7 @@ const apiMocks = vi.hoisted(() => ({
 vi.mock('@/lib/api', () => apiMocks)
 
 import { WalletProvider, useWalletContext, WALLET_POLL_INTERVAL_MS } from './WalletContext'
+import { getNetworkPassphrase } from '@/lib/stellar'
 
 const PUBLIC_KEY_A = 'GBBD47IF6LWK7P7MDEVSCWR7DPUWV3NY3DTQEVFL4NAT4AQH3ZLLFLA5'
 const PUBLIC_KEY_B = 'GDRREYWHQWJDICNH4SAH4TT2JPVYWIX6JEWAHE2W6BZDJBIJ4VSX227Z'
@@ -155,3 +156,34 @@ describe('Freighter account-drift polling', () => {
     expect(result.current.wallet.publicKey).toBe(PUBLIC_KEY_A)
   }, WALLET_POLL_INTERVAL_MS + 5_000)
 })
+
+describe('signTransaction', () => {
+  it('calls Freighter signTransaction with SDK getNetworkPassphrase for testnet and mainnet', async () => {
+    const { result } = await connectWallet(PUBLIC_KEY_A)
+    freighterMocks.signTransaction.mockResolvedValue('signed-xdr-output')
+
+    // Test on testnet
+    let signed = await act(async () => {
+      return await result.current.signTransaction('dummy-xdr-testnet')
+    })
+    expect(signed).toBe('signed-xdr-output')
+    expect(freighterMocks.signTransaction).toHaveBeenCalledWith('dummy-xdr-testnet', {
+      networkPassphrase: getNetworkPassphrase('testnet'),
+      accountToSign: PUBLIC_KEY_A,
+    })
+
+    // Switch to mainnet
+    act(() => {
+      result.current.setNetwork('mainnet')
+    })
+
+    signed = await act(async () => {
+      return await result.current.signTransaction('dummy-xdr-mainnet')
+    })
+    expect(signed).toBe('signed-xdr-output')
+    expect(freighterMocks.signTransaction).toHaveBeenCalledWith('dummy-xdr-mainnet', {
+      networkPassphrase: getNetworkPassphrase('mainnet'),
+      accountToSign: PUBLIC_KEY_A,
+    })
+  })
+})
diff --git a/src/context/WalletContext.tsx b/src/context/WalletContext.tsx
index bfb9473..90258aa 100644
--- a/src/context/WalletContext.tsx
+++ b/src/context/WalletContext.tsx
@@ -17,6 +17,7 @@ import {
 import type { Network, WalletState, AccountInfo } from '@/types'
 import { DEFAULT_SETTINGS } from '@/types'
 import { fetchAccountFromHorizon } from '@/lib/api'
+import { getNetworkPassphrase } from '@/lib/stellar'
 
 // Freighter's own popup lets the user switch accounts entirely outside this
 // app. Poll for that drift on an interval distinct from (and shorter than)
@@ -246,10 +247,7 @@ export function WalletProvider({ children }: { children: React.ReactNode }) {
       // Dynamic import to avoid SSR issues
       const { signTransaction: freighterSign } = await import('@stellar/freighter-api')
 
-      const networkPassphrase =
-        wallet.network === 'testnet'
-          ? 'Test SDF Network ; September 2015'
-          : 'Public Global Stellar Network ; September 2015'
+      const networkPassphrase = getNetworkPassphrase(wallet.network)
 
       const result = await freighterSign(xdr, {
         networkPassphrase,