diff --git a/arduino/arduino.ino b/arduino/arduino.ino
index 6fea865..c405e7c 100644
--- a/arduino/arduino.ino
+++ b/arduino/arduino.ino
@@ -44,7 +44,7 @@ void loop() {
       case 'd':
       case 'e':
       case 'f':
-        hex = hex << 2 + charMap(data);
+        hex = (hex << 2) + charMap(data);
         break;
       case 'n':
         nextColour();