diff --git a/keyboards/coseyfannitutti/mysterium/rules.mk b/keyboards/coseyfannitutti/mysterium/rules.mk
index 4147cfec965..9c518e938dc 100644
--- a/keyboards/coseyfannitutti/mysterium/rules.mk
+++ b/keyboards/coseyfannitutti/mysterium/rules.mk
@@ -2,7 +2,7 @@
 MCU = atmega32a
 
 # Processor frequency
-F_USB = 16000000
+F_CPU = 16000000
 
 # Bootloader selection
 #   Teensy       halfkay