diff --git a/servers/slapd/overlays/syncprov.c b/servers/slapd/overlays/syncprov.c
index c18e16483d..8a16cd47e3 100644
--- a/servers/slapd/overlays/syncprov.c
+++ b/servers/slapd/overlays/syncprov.c
@@ -3170,6 +3170,7 @@ syncprov_db_close(
 
 #ifdef SLAP_CONFIG_DELETE
 	if ( !slapd_shutdown ) {
+		ldap_pvt_thread_mutex_lock( &si->si_ops_mutex );
 		for ( so=si->si_ops, sonext=so;  so; so=sonext  ) {
 			SlapReply rs = {REP_RESULT};
 			rs.sr_err = LDAP_UNAVAILABLE;
@@ -3178,6 +3179,7 @@ syncprov_db_close(
 			syncprov_drop_psearch( so, 0);
 		}
 		si->si_ops=NULL;
+		ldap_pvt_thread_mutex_unlock( &si->si_ops_mutex );
 	}
 	overlay_unregister_control( be, LDAP_CONTROL_SYNC );
 #endif /* SLAP_CONFIG_DELETE */