diff --git a/servers/slapd/controls.c b/servers/slapd/controls.c
index 940ca3d464..beabe4498e 100644
--- a/servers/slapd/controls.c
+++ b/servers/slapd/controls.c
@@ -17,6 +17,7 @@
 
 #include <stdio.h>
 
+#include <ac/ctype.h>
 #include <ac/string.h>
 #include <ac/socket.h>