diff --git a/cubesatsim/cubesatsim.ino b/cubesatsim/cubesatsim.ino
index 7f6ddec4..d3c64160 100644
--- a/cubesatsim/cubesatsim.ino
+++ b/cubesatsim/cubesatsim.ino
@@ -3338,7 +3338,7 @@ void transmit_mili(int freq, float duration) {  // freq in Hz, duration in milli
 void transmit_callsign(char *callsign) {
   char de[] = "DE ";	
   char id[20];
-  strcat(id, de);
+  strcpy(id, de);
   strcat(id, callsign);
 	
   transmit_on();