diff --git a/servers/slapd/main.c b/servers/slapd/main.c
index 02dcd5009f..3fc69e45e7 100644
--- a/servers/slapd/main.c
+++ b/servers/slapd/main.c
@@ -27,6 +27,7 @@
 
 #include <stdio.h>
 
+#include <ac/ctype.h>
 #include <ac/socket.h>
 #include <ac/string.h>
 #include <ac/time.h>