diff --git a/check_login.c b/check_login.c
index 0bda894..b49a415 100644
--- a/check_login.c
+++ b/check_login.c
@@ -23,6 +23,7 @@
 
 #include <security/pam_appl.h>
 #include <stdio.h>
+#include <stdlib.h>
 
 int my_conv(int num_msg, const struct pam_message **msg, struct pam_response **resp, void *appdata_ptr);