diff --git a/platformio.ini b/platformio.ini
index d4a84f4dc8b1fcd177fe2d61f313c02f6d7a7e96..7ab6a396ed2f437fc242993fcbcd52a33c93b782 100644
--- a/platformio.ini
+++ b/platformio.ini
@@ -43,7 +43,8 @@ build_src_filter = ${fun_base.build_src_filter} +<examples/sandbox>
 build_src_filter = ${fun_base.build_src_filter} +<examples/self_modify_code>
 
 [env:uartdemo]
+build_flags = ${fun_base.build_flags} -DSTDOUT_UART
 build_src_filter = ${fun_base.build_src_filter} +<examples/uartdemo>
 
 [env:ws2812bdemo]
-build_src_filter = ${fun_base.build_src_filter} +<examples/ws2812bdemo>
\ No newline at end of file
+build_src_filter = ${fun_base.build_src_filter} +<examples/ws2812bdemo>