diff --git a/Makefile b/Makefile
index 9f0683d..ad0ec47 100644
--- a/Makefile
+++ b/Makefile
@@ -25,4 +25,9 @@ clean:
 
 distclean: clean
 
-.PHONY: all run clean distclean
+size: ponydos.asm
+	@$(NASM) -fbin -d SIZE -o ponydos_size.bin ponydos.asm
+	@wc -c ponydos_size.bin
+	@rm ponydos_size.bin
+
+.PHONY: all run clean distclean size
diff --git a/ponydos.asm b/ponydos.asm
index 4a705a0..bbc8943 100644
--- a/ponydos.asm
+++ b/ponydos.asm
@@ -437,7 +437,9 @@ hang:
 ; Padding and boot sector signature
 ; ------------------------------------------------------------------
 
+%ifndef SIZE
 times 510-($-$$) db 0
+%endif
 
 db 0x55
 db 0xaa