diff --git a/firmware/common/Makefile_inc.mk b/firmware/common/Makefile_inc.mk
index e92d8112..5e351158 100644
--- a/firmware/common/Makefile_inc.mk
+++ b/firmware/common/Makefile_inc.mk
@@ -135,7 +135,7 @@ $(BINARY).dfu: $(BINARY).bin
 	$(Q)rm -f _tmp.dfu _header.bin
 	$(Q)cp $(BINARY).bin _tmp.dfu
 	$(Q)dfu-suffix --vid=0x1fc9 --pid=0x000c --did=0x0 -s 0 -a _tmp.dfu
-	$(Q)python -c "import os.path; import struct; print('0000000: da ff ' + ' '.join(map(lambda s: '%02x' % ord(s), struct.pack('<H', os.path.getsize('$(*).bin') / 512 + 1))) + ' ff ff ff ff')" | xxd -g1 -r > _header.bin
+	$(Q)python -c "import os.path; import struct; print('0000000: da ff ' + ' '.join(map(lambda s: '%02x' % ord(s), struct.pack('<H', os.path.getsize('$(BINARY).bin') / 512 + 1))) + ' ff ff ff ff')" | xxd -g1 -r > _header.bin
 	$(Q)cat _header.bin _tmp.dfu >$(BINARY).dfu
 	$(Q)rm -f _tmp.dfu _header.bin