diff --git a/photon/libc/include/stdlib.h b/photon/libc/include/stdlib.h
index 1c161bc..c1a7d92 100644
--- a/photon/libc/include/stdlib.h
+++ b/photon/libc/include/stdlib.h
@@ -25,6 +25,7 @@ extern float strtof(const char *str, char **endptr);
 extern double strtod(const char *str, char **endptr);
 
 extern char *getenv(const char *name);
+extern int atexit(void(*fn)(void));
 
 #if defined(__cplusplus)
 } /* extern "C" */