diff --git a/builddefs/common_rules.mk b/builddefs/common_rules.mk
index d20e9ad74d..261ab7da02 100644
--- a/builddefs/common_rules.mk
+++ b/builddefs/common_rules.mk
@@ -380,33 +380,9 @@ dump_vars:
 objs-size:
 	for i in $(OBJ); do echo $$i; done | sort | xargs $(SIZE)
 
-ifeq ($(findstring avr-gcc,$(CC)),avr-gcc)
-SIZE_MARGIN = 1024
 
+# size check optionally implemented in its platform.mk
 check-size:
-	$(eval MAX_SIZE=$(shell n=`$(CC) -E -mmcu=$(MCU) -D__ASSEMBLER__ $(CFLAGS) $(OPT_DEFS) platforms/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)))
-	$(eval PERCENT_SIZE=$(shell expr $(CURRENT_SIZE) \* 100 / $(MAX_SIZE)))
-	if [ $(MAX_SIZE) -gt 0 ] && [ $(CURRENT_SIZE) -gt 0 ]; then \
-		$(SILENT) || printf "$(MSG_CHECK_FILESIZE)" | $(AWK_CMD); \
-		if [ $(CURRENT_SIZE) -gt $(MAX_SIZE) ]; then \
-			$(REMOVE) $(TARGET).$(FIRMWARE_FORMAT); \
-			$(REMOVE) $(BUILD_DIR)/$(TARGET).{hex,bin,uf2}; \
-		    printf "\n * $(MSG_FILE_TOO_BIG)"; $(PRINT_ERROR_PLAIN); \
-		else \
-		    if [ $(FREE_SIZE) -lt $(SIZE_MARGIN) ]; then \
-			$(PRINT_WARNING_PLAIN); printf " * $(MSG_FILE_NEAR_LIMIT)"; \
-		    else \
-			$(PRINT_OK); $(SILENT) || printf " * $(MSG_FILE_JUST_RIGHT)"; \
-		    fi ; \
-		fi ; \
-	fi
-else
-check-size:
-	$(SILENT) || echo "$(MSG_CHECK_FILESIZE_SKIPPED)"
-endif
 
 check-md5:
 	$(MD5SUM) $(BUILD_DIR)/$(TARGET).$(FIRMWARE_FORMAT)
diff --git a/builddefs/message.mk b/builddefs/message.mk
index bf39554dab..c7cc5171e7 100644
--- a/builddefs/message.mk
+++ b/builddefs/message.mk
@@ -91,7 +91,6 @@ MSG_AVAILABLE_KEYMAPS = $(eval $(call GENERATE_MSG_AVAILABLE_KEYMAPS))$(MSG_AVAI
 
 MSG_BOOTLOADER_NOT_FOUND_BASE = Bootloader not found. Make sure the board is in bootloader mode. See https://docs.qmk.fm/\#/newbs_flashing\n
 MSG_CHECK_FILESIZE = Checking file size of $(TARGET).$(FIRMWARE_FORMAT)
-MSG_CHECK_FILESIZE_SKIPPED = (Firmware size check does not yet support $(MCU_ORIG); skipping)
 MSG_FILE_TOO_BIG = $(ERROR_COLOR)The firmware is too large!$(NO_COLOR) $(CURRENT_SIZE)/$(MAX_SIZE) ($(OVER_SIZE) bytes over)\n
 MSG_FILE_TOO_SMALL = The firmware is too small! $(CURRENT_SIZE)/$(MAX_SIZE)\n
 MSG_FILE_JUST_RIGHT = The firmware size is fine - $(CURRENT_SIZE)/$(MAX_SIZE) ($(PERCENT_SIZE)%%, $(FREE_SIZE) bytes free)\n
diff --git a/platforms/avr/platform.mk b/platforms/avr/platform.mk
index 09028d80af..aef449cadf 100644
--- a/platforms/avr/platform.mk
+++ b/platforms/avr/platform.mk
@@ -109,6 +109,29 @@ DEBUG_HOST = localhost
 
 #============================================================================
 
+SIZE_MARGIN = 1024
+
+check-size:
+	$(eval MAX_SIZE=$(shell n=`$(CC) -E -mmcu=$(MCU) -D__ASSEMBLER__ $(CFLAGS) $(OPT_DEFS) platforms/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)))
+	$(eval PERCENT_SIZE=$(shell expr $(CURRENT_SIZE) \* 100 / $(MAX_SIZE)))
+	if [ $(MAX_SIZE) -gt 0 ] && [ $(CURRENT_SIZE) -gt 0 ]; then \
+		$(SILENT) || printf "$(MSG_CHECK_FILESIZE)" | $(AWK_CMD); \
+		if [ $(CURRENT_SIZE) -gt $(MAX_SIZE) ]; then \
+			$(REMOVE) $(TARGET).$(FIRMWARE_FORMAT); \
+			$(REMOVE) $(BUILD_DIR)/$(TARGET).{hex,bin,uf2}; \
+		    printf "\n * $(MSG_FILE_TOO_BIG)"; $(PRINT_ERROR_PLAIN); \
+		else \
+		    if [ $(FREE_SIZE) -lt $(SIZE_MARGIN) ]; then \
+			$(PRINT_WARNING_PLAIN); printf " * $(MSG_FILE_NEAR_LIMIT)"; \
+		    else \
+			$(PRINT_OK); $(SILENT) || printf " * $(MSG_FILE_JUST_RIGHT)"; \
+		    fi ; \
+		fi ; \
+	fi
+
 # Convert hex to bin.
 bin: $(BUILD_DIR)/$(TARGET).hex
 ifeq ($(BOOTLOADER),lufa-ms)