diff --git a/README_BuildProcess.md b/README_BuildProcess.md
index a1bcca3041..a8ec8c0009 100644
--- a/README_BuildProcess.md
+++ b/README_BuildProcess.md
@@ -147,6 +147,7 @@ This is a partial list of definitions that can be added in a `BOARD.py` file's `
 * `ESPR_NO_SOFTWARE_I2C` - don't build in software I2C support
 * `ESPR_NO_BLUETOOTH_MESSAGES` - don't include text versions of Bluetooth error messages (just the error number)
 * `ESPR_USE_STEPPER_TIMER` - add builtin `Stepper` class to handle higher speed stepper handling
+* `ESPR_LIMIT_DATE_RANGE` - limits the acceptable range for Date years (saves a few hundred bytes)
 
 These are set automatically when `SAVE_ON_FLASH` is set (see `jsutils.h`)