diff --git a/reactos/lib/winmm/midimap/midimap.c b/reactos/lib/winmm/midimap/midimap.c
index 227d01febf2..4c8a4a07ccc 100644
--- a/reactos/lib/winmm/midimap/midimap.c
+++ b/reactos/lib/winmm/midimap/midimap.c
@@ -26,6 +26,7 @@
 #include <stdarg.h>
 #include <string.h>
 #include <stdlib.h>
+#include <ctype.h>
 #include "windef.h"
 #include "winbase.h"
 #include "wingdi.h"