diff --git a/bacnet-stack/demo/readbdt/main.c b/bacnet-stack/demo/readbdt/main.c
index 0d07e10c..beb5a1a7 100644
--- a/bacnet-stack/demo/readbdt/main.c
+++ b/bacnet-stack/demo/readbdt/main.c
@@ -30,6 +30,7 @@
 #include <stdlib.h>
 #include <time.h>       /* for time */
 #include <errno.h>
+#include <ctype.h> /* for toupper */
 #include "bactext.h"
 #include "iam.h"
 #include "address.h"