diff --git a/cubesatsim/cubesatsim.ino b/cubesatsim/cubesatsim.ino
index b3b1f53b..3e9b6c04 100644
--- a/cubesatsim/cubesatsim.ino
+++ b/cubesatsim/cubesatsim.ino
@@ -3013,7 +3013,7 @@ void blink(int length)
   
   sleep(length/1000.0); // delay(length);              // wait for a lenth of time
 
-  digitalWrite(ED_BUILTIN, LOW);   // set the built-in LED off
+  digitalWrite(LED_BUILTIN, LOW);   // set the built-in LED off
 }
 
 void led_set(int ledPin, bool state)