diff --git a/src/main/index.ts b/src/main/index.ts
index ac456f6..d107009 100644
--- a/src/main/index.ts
+++ b/src/main/index.ts
@@ -15,7 +15,7 @@ function createWindow(): void {
     title: 'JRedisDesktop',
     backgroundColor: nativeTheme.shouldUseDarkColors ? '#0f0f1a' : '#f8fafc',
     webPreferences: {
-      preload: join(__dirname, '../preload/index.js'),
+      preload: join(__dirname, '../preload/index.mjs'),
       contextIsolation: true,
       nodeIntegration: false,
       sandbox: false,
diff --git a/src/renderer/src/stores/connection.ts b/src/renderer/src/stores/connection.ts
index 7479fc8..5ea0058 100644
--- a/src/renderer/src/stores/connection.ts
+++ b/src/renderer/src/stores/connection.ts
@@ -126,6 +126,9 @@ export const useConnectionStore = defineStore('connection', () => {
   async function testConnection(opts: {
     host: string; port: number; auth?: string; username?: string; tls?: boolean
   }): Promise<{ success: boolean; error?: string }> {
+    if (!window.electronAPI) {
+      return { success: false, error: 'Electron API not ready' }
+    }
     const testId = `test_${Date.now()}`
     try {
       const result = await window.electronAPI.redis.connect(testId, {