diff --git a/platform/cooja/dev/rs232.c b/platform/cooja/dev/rs232.c
index 51ee5b6a9..08257b555 100644
--- a/platform/cooja/dev/rs232.c
+++ b/platform/cooja/dev/rs232.c
@@ -46,6 +46,7 @@ char simSerialReceivingFlag;
 
 static int (* input_handler)(unsigned char) = NULL;
 
+void simlog_char(char c);
 /*-----------------------------------------------------------------------------------*/
 void rs232_init(void) { }
 /*-----------------------------------------------------------------------------------*/