diff --git a/common_features.mk b/common_features.mk
index 7ed77a889d..32028c8af5 100644
--- a/common_features.mk
+++ b/common_features.mk
@@ -450,6 +450,7 @@ ifeq ($(strip $(SPLIT_KEYBOARD)), yes)
         endif
 
         SERIAL_DRIVER ?= bitbang
+        OPT_DEFS += -DSERIAL_DRIVER_$(strip $(shell echo $(SERIAL_DRIVER) | tr '[:lower:]' '[:upper:]'))
         ifeq ($(strip $(SERIAL_DRIVER)), bitbang)
             QUANTUM_LIB_SRC += serial.c
         else