diff --git a/libraries/libldap/os-ip.c b/libraries/libldap/os-ip.c
index d2d0fac434..bd4596105d 100644
--- a/libraries/libldap/os-ip.c
+++ b/libraries/libldap/os-ip.c
@@ -145,6 +145,10 @@ ldap_int_prepare_socket(LDAP *ld, int s, int proto )
 		if ( ld->ld_options.ldo_keepalive_idle > 0 )
 		{
 #ifdef TCP_KEEPIDLE
+/* AIX uses protocol numbers for everything besides SOL_SOCKET */
+#ifndef SOL_TCP
+#define	SOL_TCP	IPPROTO_TCP
+#endif
 			if ( setsockopt( s, SOL_TCP, TCP_KEEPIDLE,
 					(void*) &ld->ld_options.ldo_keepalive_idle,
 					sizeof(ld->ld_options.ldo_keepalive_idle) ) == AC_SOCKET_ERROR )