2 files changed, 5 insertions, 0 deletions
diff --git a/cores/arduino/Arduino.h b/cores/arduino/Arduino.h
index 630f0d6..ac775f1 100644
--- a/cores/arduino/Arduino.h
+++ b/cores/arduino/Arduino.h
@@ -120,6 +120,8 @@ typedef uint8_t byte;
 void init(void);
 void initVariant(void);
 
+int atexit(void (*func)()) __attribute__((weak));
+
 void pinMode(uint8_t, uint8_t);
 void digitalWrite(uint8_t, uint8_t);
 int digitalRead(uint8_t);
diff --git a/cores/arduino/main.cpp b/cores/arduino/main.cpp
index 091c365..a60980d 100644
--- a/cores/arduino/main.cpp
+++ b/cores/arduino/main.cpp
@@ -19,6 +19,9 @@
 
 #include <Arduino.h>
 
+//Declared weak in Arduino.h to allow user redefinitions.
+int atexit(void (*func)()) { return 0; }
+
 // Weak empty variant initialization function.
 // May be redefined by variant files.
 void initVariant() __attribute__((weak));