diff --git a/user_io.cpp b/user_io.cpp
index 2c15ee5..9fb7ab6 100644
--- a/user_io.cpp
+++ b/user_io.cpp
@@ -567,13 +567,15 @@ int GetUARTMode()
 
 void SetUARTMode(int mode)
 {
+	mode &= 0xFF;
+
 	if (is_x86()) x86_set_uart_mode(mode != 3);
 
 	MakeFile("/tmp/CORENAME", user_io_get_core_name_ex());
 	MakeFile("/tmp/UART_SPEED", is_st() ? "19200" : (is_x86() && (user_io_8bit_set_status(0, 0, 0) & (1 << 10))) ? "4000000" : "115200");
 
 	char cmd[32];
-	sprintf(cmd, "uartmode %d", mode & 0xFF);
+	sprintf(cmd, "uartmode %d", mode);
 	system(cmd);
 	set_uart_alt();
 }