diff --git a/reactos/lib/wininet/ftp.c b/reactos/lib/wininet/ftp.c
index 77f16a0d075..e9093bd8ea3 100644
--- a/reactos/lib/wininet/ftp.c
+++ b/reactos/lib/wininet/ftp.c
@@ -34,6 +34,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <ctype.h>
 #include <sys/types.h>
 #ifdef HAVE_SYS_SOCKET_H
 # include <sys/socket.h>