diff --git a/packages/vite/src/node/__tests__/config.spec.ts b/packages/vite/src/node/__tests__/config.spec.ts
index 30c3a4152f7b8a..719f3601ccb5e6 100644
--- a/packages/vite/src/node/__tests__/config.spec.ts
+++ b/packages/vite/src/node/__tests__/config.spec.ts
@@ -989,6 +989,30 @@ describe('mergeConfig', () => {
     }
   })
 
+  test('mergeConfig handles server.hmr when server.ws is false', () => {
+    const mergedConfig = mergeConfig(
+      {
+        server: {
+          ws: false,
+          hmr: { host: 'localhost' },
+        },
+      },
+      {
+        server: {
+          hmr: { port: 5173 },
+        },
+      },
+    )
+
+    expect(mergedConfig.server).toMatchObject({
+      ws: false,
+      hmr: {
+        host: 'localhost',
+        port: 5173,
+      },
+    })
+  })
+
   test('syncs `server.hmr.*` to `server.ws.*`', () => {
     const baseConfig = defineConfig({
       server: {
diff --git a/packages/vite/src/node/utils.ts b/packages/vite/src/node/utils.ts
index cc064f8f655561..c587349591a473 100644
--- a/packages/vite/src/node/utils.ts
+++ b/packages/vite/src/node/utils.ts
@@ -1479,11 +1479,10 @@ function mergeConfigRecursively(
   }
   if (rootPath === 'server.hmr') {
     for (const key of wsOptionKeys) {
-      Object.defineProperty(
-        merged,
-        key,
-        Object.getOwnPropertyDescriptor(defaults, key)!,
-      )
+      const descriptor = Object.getOwnPropertyDescriptor(defaults, key)
+      if (descriptor) {
+        Object.defineProperty(merged, key, descriptor)
+      }
     }
   }