diff --git a/cores/esp8266/Esp.cpp b/cores/esp8266/Esp.cpp
index 1fd8b2c52d..554e4f8a45 100644
--- a/cores/esp8266/Esp.cpp
+++ b/cores/esp8266/Esp.cpp
@@ -183,6 +183,11 @@ uint32_t EspClass::getFreeContStack()
     return cont_get_free_stack(g_pcont);
 }
 
+uint32_t EspClass::getFreeSysStack()
+{
+	register volatile uint32_t stackAddress asm("a1");
+	return stackAddress-SYSTEM_STACK_END_ADDRESS;
+}
 uint32_t EspClass::getChipId(void)
 {
     return system_get_chip_id();
diff --git a/cores/esp8266/Esp.h b/cores/esp8266/Esp.h
index d058f2225c..b05f7817f8 100644
--- a/cores/esp8266/Esp.h
+++ b/cores/esp8266/Esp.h
@@ -65,6 +65,9 @@ enum RFMode {
 #define WAKE_NO_RFCAL    RF_NO_CAL
 #define WAKE_RF_DISABLED RF_DISABLED
 
+// for getFreeSysStack
+#define SYSTEM_STACK_END_ADDRESS 0x3FFFC000
+
 enum ADCMode {
     ADC_TOUT = 33,
     ADC_TOUT_3V3 = 33,
@@ -111,6 +114,7 @@ class EspClass {
         void getHeapStats(uint32_t* free = nullptr, uint16_t* max = nullptr, uint8_t* frag = nullptr);
 
         uint32_t getFreeContStack();
+        uint32_t getFreeSysStack();
 
         const char * getSdkVersion();
         String getCoreVersion();