Change handling of CUSTOM_MATRIX in common_features.mk slightly.

common_features.mk

@@ -254,15 +254,12 @@ QUANTUM_SRC:= \
     $(QUANTUM_DIR)/keymap_common.c \
     $(QUANTUM_DIR)/keycode_config.c
 
-ifneq ($(strip $(CUSTOM_MATRIX)), yes)
-    ifeq ($(strip $(SPLIT_KEYBOARD)), yes)
-        QUANTUM_SRC += $(QUANTUM_DIR)/split_common/matrix.c
-    else
-        QUANTUM_SRC += $(QUANTUM_DIR)/matrix.c
-    endif
-endif
-
 ifeq ($(strip $(SPLIT_KEYBOARD)), yes)
+    ifneq ($(strip $(CUSTOM_MATRIX)), yes)
+       QUANTUM_SRC += $(QUANTUM_DIR)/split_common/matrix.c
+       # Do not use $(QUANTUM_DIR)/matrix.c.
+       CUSTOM_MATRIX=yes
+    endif
     OPT_DEFS += -DSPLIT_KEYBOARD
     QUANTUM_SRC += $(QUANTUM_DIR)/split_common/split_flags.c \
                 $(QUANTUM_DIR)/split_common/split_util.c
@@ -270,3 +267,7 @@ ifeq ($(strip $(SPLIT_KEYBOARD)), yes)
     QUANTUM_LIB_SRC += $(QUANTUM_DIR)/split_common/serial.c
     COMMON_VPATH += $(QUANTUM_PATH)/split_common
 endif
+
+ifneq ($(strip $(CUSTOM_MATRIX)), yes)
+    QUANTUM_SRC += $(QUANTUM_DIR)/matrix.c
+endif