diff --git a/ports/unix/main.c b/ports/unix/main.c
index b69df90354..55bdc22082 100644
--- a/ports/unix/main.c
+++ b/ports/unix/main.c
@@ -690,6 +690,13 @@ MP_NOINLINE int main_(int argc, char **argv) {
     MP_STATE_THREAD(prof_trace_callback) = MP_OBJ_NULL;
     #endif
 
+    #if MICROPY_PY_SYS_ATEXIT
+    // Beware, the sys.settrace callback should be disabled before running sys.atexit.
+    if (mp_obj_is_callable(MP_STATE_VM(sys_exitfunc))) {
+        mp_call_function_0(MP_STATE_VM(sys_exitfunc));
+    }
+    #endif
+
     #if MICROPY_PY_MICROPYTHON_MEM_INFO
     if (mp_verbose_flag) {
         mp_micropython_mem_info(0, NULL);
diff --git a/py/modsys.c b/py/modsys.c
index 1e31a04d27..cbd1712920 100644
--- a/py/modsys.c
+++ b/py/modsys.c
@@ -166,6 +166,16 @@ STATIC mp_obj_t mp_sys_getsizeof(mp_obj_t obj) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(mp_sys_getsizeof_obj, mp_sys_getsizeof);
 #endif
 
+#if MICROPY_PY_SYS_ATEXIT
+// atexit(callback): Callback is called when sys.exit is called.
+STATIC mp_obj_t mp_sys_atexit(mp_obj_t obj) {
+    mp_obj_t old = MP_STATE_VM(sys_exitfunc);
+    MP_STATE_VM(sys_exitfunc) = obj;
+    return old;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(mp_sys_atexit_obj, mp_sys_atexit);
+#endif
+
 #if MICROPY_PY_SYS_SETTRACE
 // settrace(tracefunc): Set the system’s trace function.
 STATIC mp_obj_t mp_sys_settrace(mp_obj_t obj) {
@@ -227,6 +237,14 @@ STATIC const mp_rom_map_elem_t mp_module_sys_globals_table[] = {
     #if MICROPY_PY_SYS_GETSIZEOF
     { MP_ROM_QSTR(MP_QSTR_getsizeof), MP_ROM_PTR(&mp_sys_getsizeof_obj) },
     #endif
+
+    /*
+     * Extensions to CPython
+     */
+
+    #if MICROPY_PY_SYS_ATEXIT
+    { MP_ROM_QSTR(MP_QSTR_atexit), MP_ROM_PTR(&mp_sys_atexit_obj) },
+    #endif
 };
 
 STATIC MP_DEFINE_CONST_DICT(mp_module_sys_globals, mp_module_sys_globals_table);
diff --git a/py/mpconfig.h b/py/mpconfig.h
index 8419a50d5e..2cd2a0d356 100644
--- a/py/mpconfig.h
+++ b/py/mpconfig.h
@@ -1311,6 +1311,11 @@ typedef double mp_float_t;
 #define MICROPY_PY_SYS_EXIT (1)
 #endif
 
+// Whether to provide "sys.atexit" function (MicroPython extension)
+#ifndef MICROPY_PY_SYS_ATEXIT
+#define MICROPY_PY_SYS_ATEXIT (0)
+#endif
+
 // Whether to provide "sys.settrace" function
 #ifndef MICROPY_PY_SYS_SETTRACE
 #define MICROPY_PY_SYS_SETTRACE (0)
diff --git a/py/mpstate.h b/py/mpstate.h
index e868a773bf..423463109d 100644
--- a/py/mpstate.h
+++ b/py/mpstate.h
@@ -157,6 +157,11 @@ typedef struct _mp_state_vm_t {
     mp_obj_base_t *cur_exception;
     #endif
 
+    #if MICROPY_PY_SYS_ATEXIT
+    // exposed through sys.atexit function
+    mp_obj_t sys_exitfunc;
+    #endif
+
     // dictionary for the __main__ module
     mp_obj_dict_t dict_main;
 
diff --git a/py/runtime.c b/py/runtime.c
index ba0d59dffa..ceb5e83b14 100644
--- a/py/runtime.c
+++ b/py/runtime.c
@@ -130,6 +130,10 @@ void mp_init(void) {
         sizeof(MP_STATE_VM(fs_user_mount)) - MICROPY_FATFS_NUM_PERSISTENT);
     #endif
 
+    #if MICROPY_PY_SYS_ATEXIT
+    MP_STATE_VM(sys_exitfunc) = mp_const_none;
+    #endif
+
     #if MICROPY_PY_SYS_SETTRACE
     MP_STATE_THREAD(prof_trace_callback) = MP_OBJ_NULL;
     MP_STATE_THREAD(prof_callback_is_executing) = false;