diff --git a/radio/src/CMakeLists.txt b/radio/src/CMakeLists.txt
index 4a55a63e0..c834933ed 100644
--- a/radio/src/CMakeLists.txt
+++ b/radio/src/CMakeLists.txt
@@ -9,7 +9,7 @@ option(CURVES "Curves" ON)
 option(GVARS "Global variables")
 option(GUI "GUI enabled" ON)
 option(SPLASH "Splash enabled" ON)
-option(PPM_UNIT "PPM display unit (US/PERCENT_PREC1/PERCENT_PREC0)" PERCENT_PREC1)
+set(PPM_UNIT "PERCENT_PREC1" CACHE STRING "PPM display unit (US/PERCENT_PREC1/PERCENT_PREC0)")
 option(PPM_CENTER_ADJUSTABLE "PPM center adjustable" OFF)
 option(PPM_LIMITS_SYMETRICAL "PPM limits symetrical" OFF)
 option(OVERRIDE_CHANNEL_FUNCTION "OverrideChannel function available" ON)