diff --git a/tmk_core/avr.mk b/tmk_core/avr.mk
index 521305f1b4f..2ba193c7622 100644
--- a/tmk_core/avr.mk
+++ b/tmk_core/avr.mk
@@ -295,7 +295,7 @@ ifneq ($(strip $(BOOTLOADER)), qmk-dfu)
 endif
 	make -C lib/lufa/Bootloaders/DFU/ clean
 	$(QMK_BIN) generate-dfu-header --quiet --keyboard $(KEYBOARD) --output lib/lufa/Bootloaders/DFU/Keyboard.h
-	$(eval MAX_SIZE=$(shell n=`$(CC) -E -mmcu=$(MCU) $(CFLAGS) $(OPT_DEFS) tmk_core/common/avr/bootloader_size.c 2> /dev/null | sed -ne 's/\r//;/^#/n;/^AVR_SIZE:/,$${s/^AVR_SIZE: //;p;}'` && echo $$(($$n)) || echo 0))
+	$(eval MAX_SIZE=$(shell n=`$(CC) -E -mmcu=$(MCU) -D__ASSEMBLER__ $(CFLAGS) $(OPT_DEFS) tmk_core/common/avr/bootloader_size.c 2> /dev/null | sed -ne 's/\r//;/^#/n;/^AVR_SIZE:/,$${s/^AVR_SIZE: //;p;}'` && echo $$(($$n)) || echo 0))
 	$(eval PROGRAM_SIZE_KB=$(shell n=`expr $(MAX_SIZE) / 1024` && echo $$(($$n)) || echo 0))
 	$(eval BOOT_SECTION_SIZE_KB=$(shell n=`expr  $(BOOTLOADER_SIZE) / 1024` && echo $$(($$n)) || echo 0))
 	$(eval FLASH_SIZE_KB=$(shell n=`expr $(PROGRAM_SIZE_KB) + $(BOOT_SECTION_SIZE_KB)` && echo $$(($$n)) || echo 0))
diff --git a/tmk_core/rules.mk b/tmk_core/rules.mk
index fc2dc68be22..597f7aa8272 100644
--- a/tmk_core/rules.mk
+++ b/tmk_core/rules.mk
@@ -458,7 +458,7 @@ ifeq ($(findstring avr-gcc,$(CC)),avr-gcc)
 SIZE_MARGIN = 1024
 
 check-size:
-	$(eval MAX_SIZE=$(shell n=`$(CC) -E -mmcu=$(MCU) $(CFLAGS) $(OPT_DEFS) tmk_core/common/avr/bootloader_size.c 2> /dev/null | sed -ne 's/\r//;/^#/n;/^AVR_SIZE:/,$${s/^AVR_SIZE: //;p;}'` && echo $$(($$n)) || echo 0))
+	$(eval MAX_SIZE=$(shell n=`$(CC) -E -mmcu=$(MCU) -D__ASSEMBLER__ $(CFLAGS) $(OPT_DEFS) tmk_core/common/avr/bootloader_size.c 2> /dev/null | sed -ne 's/\r//;/^#/n;/^AVR_SIZE:/,$${s/^AVR_SIZE: //;p;}'` && echo $$(($$n)) || echo 0))
 	$(eval CURRENT_SIZE=$(shell if [ -f $(BUILD_DIR)/$(TARGET).hex ]; then $(SIZE) --target=$(FORMAT) $(BUILD_DIR)/$(TARGET).hex | $(AWK) 'NR==2 {print $$4}'; else printf 0; fi))
 	$(eval FREE_SIZE=$(shell expr $(MAX_SIZE) - $(CURRENT_SIZE)))
 	$(eval OVER_SIZE=$(shell expr $(CURRENT_SIZE) - $(MAX_SIZE)))