diff --git a/src/dos/cdrom_aspi_win32.cpp b/src/dos/cdrom_aspi_win32.cpp
index cd63999b..33d8c2a2 100644
--- a/src/dos/cdrom_aspi_win32.cpp
+++ b/src/dos/cdrom_aspi_win32.cpp
@@ -18,6 +18,8 @@
 
 #if defined (WIN32)
 
+#include <ctype.h>
+
 #include "cdrom.h"
 #include "scsidefs.h"			// Aspi stuff
 #include "dosbox.h"