diff --git a/satip.c b/satip.c
index 68cc613..ef930c6 100644
--- a/satip.c
+++ b/satip.c
@@ -5,6 +5,7 @@
  *
  */
 
+#include <ctype.h>
 #include <getopt.h>
 #include <vdr/plugin.h>
 #include "common.h"