diff --git a/cores/esp8266/Esp.cpp b/cores/esp8266/Esp.cpp
index 21ffe880e..db29ec599 100644
--- a/cores/esp8266/Esp.cpp
+++ b/cores/esp8266/Esp.cpp
@@ -264,11 +264,12 @@ uint8_t EspClass::getBootMode(void)
     return system_get_boot_mode();
 }
 
+#ifndef F_CPU
 uint8_t EspClass::getCpuFreqMHz(void)
 {
     return system_get_cpu_freq();
 }
-
+#endif
 
 uint32_t EspClass::getFlashChipId(void)
 {
diff --git a/cores/esp8266/Esp.h b/cores/esp8266/Esp.h
index f4529c839..01327747e 100644
--- a/cores/esp8266/Esp.h
+++ b/cores/esp8266/Esp.h
@@ -157,7 +157,14 @@ class EspClass {
         uint8_t getBootVersion();
         uint8_t getBootMode();
 
+#if defined(F_CPU) || defined(CORE_MOCK)
+        constexpr uint8_t getCpuFreqMHz() const
+        {
+            return clockCyclesPerMicrosecond();
+        }
+#else
         uint8_t getCpuFreqMHz();
+#endif
 
         uint32_t getFlashChipId();
         uint8_t getFlashChipVendorId();
@@ -201,6 +208,7 @@ class EspClass {
 };
 
 #ifndef CORE_MOCK
+
 uint32_t EspClass::getCycleCount()
 {
     return esp_get_cycle_count();
diff --git a/cores/esp8266/PolledTimeout.h b/cores/esp8266/PolledTimeout.h
index fe9c9ca4b..715564a8e 100644
--- a/cores/esp8266/PolledTimeout.h
+++ b/cores/esp8266/PolledTimeout.h
@@ -76,7 +76,7 @@ struct TimeSourceCycles
 
   using timeType = decltype(ESP.getCycleCount());
   static timeType time() {return ESP.getCycleCount();}
-  static constexpr timeType ticksPerSecond    = F_CPU;     // 80'000'000 or 160'000'000 Hz
+  static constexpr timeType ticksPerSecond    = ESP.getCpuFreqMHz() * 1000000UL;     // 80'000'000 or 160'000'000 Hz
   static constexpr timeType ticksPerSecondMax = 160000000; // 160MHz
 };
 
diff --git a/cores/esp8266/core_esp8266_main.cpp b/cores/esp8266/core_esp8266_main.cpp
index a95c4b2c1..0ec4f1f3b 100644
--- a/cores/esp8266/core_esp8266_main.cpp
+++ b/cores/esp8266/core_esp8266_main.cpp
@@ -81,14 +81,25 @@ void initVariant() __attribute__((weak));
 void initVariant() {
 }
 
-void preloop_update_frequency() __attribute__((weak));
-void preloop_update_frequency() {
+extern "C" void __preloop_update_frequency() {
 #if defined(F_CPU) && (F_CPU == 160000000L)
-    REG_SET_BIT(0x3ff00014, BIT(0));
     ets_update_cpu_frequency(160);
+    CPU2X |= 1UL;
+#elif defined(F_CPU)
+    ets_update_cpu_frequency(80);
+    CPU2X &= ~1UL;
+#elif !defined(F_CPU)
+    if (system_get_cpu_freq() == 160) {
+        CPU2X |= 1UL;
+    }
+    else {
+        CPU2X &= ~1UL;
+    }
 #endif
 }
 
+extern "C" void preloop_update_frequency() __attribute__((weak, alias("__preloop_update_frequency")));
+
 extern "C" bool can_yield() {
   return cont_can_yield(g_pcont);
 }
diff --git a/tests/host/common/MockEsp.cpp b/tests/host/common/MockEsp.cpp
index c5ca502ed..0854bdcd7 100644
--- a/tests/host/common/MockEsp.cpp
+++ b/tests/host/common/MockEsp.cpp
@@ -118,11 +118,6 @@ uint32_t EspClass::getFreeSketchSpace()
   return 4 * 1024 * 1024;
 }
 
-uint8_t EspClass::getCpuFreqMHz()
-{
-  return F_CPU / 1000000;
-}
-
 const char *EspClass::getSdkVersion()
 {
   return "2.5.0";