diff --git a/servers/slapd/back-ldbm/id2children.c b/servers/slapd/back-ldbm/id2children.c
index b8272b87a1..522e3d2733 100644
--- a/servers/slapd/back-ldbm/id2children.c
+++ b/servers/slapd/back-ldbm/id2children.c
@@ -3,6 +3,7 @@
 #include "portable.h"
 
 #include <stdio.h>
+#include <ac/string.h>
 
 #include <ac/socket.h>