diff --git a/esp8266/Makefile b/esp8266/Makefile
index 50862623d56b66f3323255a6e9ee1e0312c7a46f..306935210e535491d6c44f38155a56db6fd0be5d 100644
--- a/esp8266/Makefile
+++ b/esp8266/Makefile
@@ -23,7 +23,9 @@ INC += -I../lib/timeutils
 INC += -I$(BUILD)
 INC += -I$(ESP_SDK)/include
 
-UART_OS = 1
+# UART for "os" messages. 0 is normal UART as used by MicroPython REPL,
+# 1 is debug UART (tx only).
+UART_OS = 0
 
 CFLAGS_XTENSA = -fsingle-precision-constant -Wdouble-promotion \
 	-D__ets__ -DICACHE_FLASH \
diff --git a/esp8266/uart.c b/esp8266/uart.c
index 942c397e9090614dc5ca2378e559157a1cecf357..4f45a952ba81ce92d2527ce80d481d36d03037a4 100644
--- a/esp8266/uart.c
+++ b/esp8266/uart.c
@@ -205,7 +205,7 @@ void ICACHE_FLASH_ATTR uart_init(UartBautRate uart0_br, UartBautRate uart1_br) {
     uart_config(UART1);
     ETS_UART_INTR_ENABLE();
 
-    // install uart1 putc callback
+    // install handler for "os" messages
     os_install_putc1((void *)uart_os_write_char);
 }