diff --git a/auth-pam.c b/auth-pam.c
index d3f400bc3..ee9d2c7e9 100644
--- a/auth-pam.c
+++ b/auth-pam.c
@@ -56,6 +56,7 @@
 #include <errno.h>
 #include <signal.h>
 #include <stdarg.h>
+#include <stdlib.h>
 #include <string.h>
 #include <unistd.h>