diff --git a/cores/esp32/HardwareSerial.cpp b/cores/esp32/HardwareSerial.cpp
index 33014f13a66..c5c24ab5a34 100644
--- a/cores/esp32/HardwareSerial.cpp
+++ b/cores/esp32/HardwareSerial.cpp
@@ -2,6 +2,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <inttypes.h>
+#include <ctime>
 
 #include "pins_arduino.h"
 #include "HardwareSerial.h"