diff --git a/libraries/libldap_r/threads.c b/libraries/libldap_r/threads.c
index 3ac48498e7..e14fdb1e2c 100644
--- a/libraries/libldap_r/threads.c
+++ b/libraries/libldap_r/threads.c
@@ -16,6 +16,7 @@
 
 #include <ac/stdlib.h>
 #include <ac/string.h>
+#include <ac/unistd.h>
 
 #include "ldap_pvt_thread.h"