diff --git a/nemu/src/device/timer.c b/nemu/src/device/timer.c
index a582580..3fe5b1c 100644
--- a/nemu/src/device/timer.c
+++ b/nemu/src/device/timer.c
@@ -21,7 +21,7 @@ static uint32_t *rtc_port_base = NULL;
 
 static void rtc_io_handler(uint32_t offset, int len, bool is_write) {
   assert(offset == 0 || offset == 4);
-  if (!is_write && offset == 4) {
+  if (!is_write && offset == 0) {
     uint64_t us = get_time();
     printf("rtc_io_handle %ld\n", us);
     rtc_port_base[0] = (uint32_t)us;