diff --git a/libraries/libldap/os-ip.c b/libraries/libldap/os-ip.c
index e1ebac2661..b56809cda4 100644
--- a/libraries/libldap/os-ip.c
+++ b/libraries/libldap/os-ip.c
@@ -293,6 +293,8 @@ do_ldap_select( LDAP *ld, struct timeval *timeout )
 		tblsize = sysconf( _SC_OPEN_MAX );
 #elif defined( HAVE_GETDTABLESIZE )
 		tblsize = getdtablesize();
+#else
+		tblsize = FD_SETSIZE;
 #endif /* !USE_SYSCONF */
 
 #ifdef FD_SETSIZE