diff --git a/src/mcp/tools/device/__tests__/build_device.test.ts b/src/mcp/tools/device/__tests__/build_device.test.ts
index 7ac5812b..4e4d0175 100644
--- a/src/mcp/tools/device/__tests__/build_device.test.ts
+++ b/src/mcp/tools/device/__tests__/build_device.test.ts
@@ -346,5 +346,32 @@ describe('build_device plugin', () => {
       ]);
       expect(spy.commandCalls[0].logPrefix).toBe('iOS Device Build');
     });
+
+    it('should target watchOS platform when platform=watchOS is provided', async () => {
+      const spy = createSpyExecutor();
+
+      const { result } = await runToolLogic(() =>
+        buildDeviceLogic(
+          {
+            projectPath: '/path/to/MyWatchApp.xcodeproj',
+            scheme: 'MyWatchApp',
+            platform: 'watchOS',
+          },
+          spy.executor,
+        ),
+      );
+
+      expect(spy.commandCalls).toHaveLength(1);
+      const args = spy.commandCalls[0].args;
+      const destinationIndex = args.indexOf('-destination');
+      expect(destinationIndex).toBeGreaterThan(-1);
+      expect(args[destinationIndex + 1]).toBe('generic/platform=watchOS');
+      expect(spy.commandCalls[0].logPrefix).toBe('watchOS Device Build');
+      expect(result.nextStepParams).toEqual(
+        expect.objectContaining({
+          get_device_app_path: expect.objectContaining({ platform: 'watchOS' }),
+        }),
+      );
+    });
   });
 });
diff --git a/src/mcp/tools/device/build_device.ts b/src/mcp/tools/device/build_device.ts
index 2a5e4095..f5787f61 100644
--- a/src/mcp/tools/device/build_device.ts
+++ b/src/mcp/tools/device/build_device.ts
@@ -46,11 +46,11 @@ const baseSchemaObject = z.object({
   projectPath: z.string().optional().describe('Path to the .xcodeproj file'),
   workspacePath: z.string().optional().describe('Path to the .xcworkspace file'),
   scheme: z.string().describe('The scheme to build'),
+  platform: devicePlatformSchema,
   configuration: z.string().optional().describe('Build configuration (Debug, Release)'),
   derivedDataPath: z.string().optional(),
   extraArgs: z.array(z.string()).optional(),
   preferXcodebuild: z.boolean().optional(),
-  platform: devicePlatformSchema,
 });
 
 const buildDeviceSchema = z.preprocess(
@@ -128,6 +128,9 @@ export async function buildDeviceLogic(
         ...(params.derivedDataPath !== undefined
           ? { derivedDataPath: params.derivedDataPath }
           : {}),
+        ...(params.platform !== undefined
+          ? { platform: String(mapDevicePlatform(params.platform)) }
+          : {}),
       },
     };
   }