diff --git a/esp8266/esp_mphal.c b/esp8266/esp_mphal.c
index 7c9590a..b075523 100644
--- a/esp8266/esp_mphal.c
+++ b/esp8266/esp_mphal.c
@@ -117,7 +117,7 @@
 }
 
 uint32_t mp_hal_ticks_ms(void) {
-    return system_get_time() / 1000;
+    return ((uint64_t)system_time_high_word << 32 | (uint64_t)system_get_time()) / 1000;
 }
 
 uint32_t mp_hal_ticks_us(void) {
diff --git a/esp8266/ets_alt_task.c b/esp8266/ets_alt_task.c
index ef1d8aa..6434f23 100644
--- a/esp8266/ets_alt_task.c
+++ b/esp8266/ets_alt_task.c
@@ -110,10 +110,22 @@
 
 int ets_loop_iter_disable = 0;
 
+// to implement a 64-bit wide microsecond counter
+static uint32_t system_time_prev = 0;
+uint32_t system_time_high_word = 0;
+
 bool ets_loop_iter(void) {
     if (ets_loop_iter_disable) {
         return false;
     }
+
+    // handle overflow of system microsecond counter
+    uint32_t system_time_cur = system_get_time();
+    if (system_time_cur < system_time_prev) {
+        system_time_high_word += 1; // record overflow of low 32-bits
+    }
+    system_time_prev = system_time_cur;
+
     //static unsigned cnt;
     bool progress = false;
     for (volatile struct task_entry *t = emu_tasks; t < &emu_tasks[MP_ARRAY_SIZE(emu_tasks)]; t++) {
diff --git a/esp8266/ets_alt_task.h b/esp8266/ets_alt_task.h
index 4b5ba26..dba0c5f 100644
--- a/esp8266/ets_alt_task.h
+++ b/esp8266/ets_alt_task.h
@@ -1,2 +1,4 @@
 extern int ets_loop_iter_disable;
+extern uint32_t system_time_high_word;
+
 bool ets_loop_iter(void);