diff --git a/src/plugins/auth-pam/auth-pam.c b/src/plugins/auth-pam/auth-pam.c
index f893b51f..70339445 100644
--- a/src/plugins/auth-pam/auth-pam.c
+++ b/src/plugins/auth-pam/auth-pam.c
@@ -47,6 +47,7 @@
 #include <fcntl.h>
 #include <signal.h>
 #include <syslog.h>
+#include <limits.h>
 #include "utils.h"
 
 #include <openvpn-plugin.h>