diff --git a/cores/esp8266/Arduino.h b/cores/esp8266/Arduino.h
index acf5fbdef..a4e00ec73 100644
--- a/cores/esp8266/Arduino.h
+++ b/cores/esp8266/Arduino.h
@@ -204,6 +204,7 @@ void setup(void);
 void loop(void);
 
 void yield(void);
+
 void optimistic_yield(uint32_t interval_us);
 
 #define _PORT_GPIO16    1
diff --git a/cores/esp8266/core_esp8266_main.cpp b/cores/esp8266/core_esp8266_main.cpp
index 850d9b95a..a95c4b2c1 100644
--- a/cores/esp8266/core_esp8266_main.cpp
+++ b/cores/esp8266/core_esp8266_main.cpp
@@ -37,7 +37,6 @@ extern "C" {
 
 #define LOOP_TASK_PRIORITY 1
 #define LOOP_QUEUE_SIZE    1
-#define OPTIMISTIC_YIELD_TIME_US 16000
 
 extern "C" void call_user_start();
 extern void loop();
@@ -58,7 +57,7 @@ cont_t* g_pcont __attribute__((section(".noinit")));
 static os_event_t s_loop_queue[LOOP_QUEUE_SIZE];
 
 /* Used to implement optimistic_yield */
-static uint32_t s_micros_at_task_start;
+static uint32_t s_cycles_at_yield_start;
 
 /* For ets_intr_lock_nest / ets_intr_unlock_nest
  * Max nesting seen by SDK so far is 2.
@@ -97,6 +96,7 @@ extern "C" bool can_yield() {
 static inline void esp_yield_within_cont() __attribute__((always_inline));
 static void esp_yield_within_cont() {
         cont_yield(g_pcont);
+        s_cycles_at_yield_start = ESP.getCycleCount();
         run_scheduled_recurrent_functions();
 }
 
@@ -125,14 +125,19 @@ extern "C" void __yield() {
 extern "C" void yield(void) __attribute__ ((weak, alias("__yield")));
 
 extern "C" void optimistic_yield(uint32_t interval_us) {
-    if (can_yield() &&
-        (system_get_time() - s_micros_at_task_start) > interval_us)
+    const uint32_t intvl_cycles = interval_us *
+#if defined(F_CPU)
+        clockCyclesPerMicrosecond();
+#else
+        ESP.getCpuFreqMHz();
+#endif
+    if ((ESP.getCycleCount() - s_cycles_at_yield_start) > intvl_cycles &&
+        can_yield())
     {
         yield();
     }
 }
 
-
 // Replace ets_intr_(un)lock with nestable versions
 extern "C" void IRAM_ATTR ets_intr_lock() {
   if (ets_intr_lock_stack_ptr < ETS_INTR_LOCK_NEST_MAX)
@@ -183,7 +188,7 @@ static void loop_wrapper() {
 
 static void loop_task(os_event_t *events) {
     (void) events;
-    s_micros_at_task_start = system_get_time();
+    s_cycles_at_yield_start = ESP.getCycleCount();
     cont_run(g_pcont, &loop_wrapper);
     if (cont_check(g_pcont) != 0) {
         panic();
@@ -211,7 +216,7 @@ extern void __unhandled_exception(const char *str);
 static void  __unhandled_exception_cpp()
 {
 #ifndef __EXCEPTIONS
-	abort();
+    abort();
 #else
     static bool terminating;
     if (terminating)