diff --git a/satip.c b/satip.c
index e906d69..7529d09 100644
--- a/satip.c
+++ b/satip.c
@@ -5,6 +5,7 @@
  *
  */
 
+#include <ctype.h>
 #include <getopt.h>
 #include <vdr/plugin.h>
 #include "common.h"