diff --git a/boot/makefile b/boot/makefile
index 94c9a8f..f36e514 100644
--- a/boot/makefile
+++ b/boot/makefile
@@ -8,22 +8,22 @@
 production:     fat12com.bin fat16com.bin fat32chs.bin fat32lba.bin oemfat12.bin oemfat16.bin
 
 fat12com.bin:    boot.asm
-		$(NASM) -dISFAT12 boot.asm -l$*.lst -ofat12com.bin
+		$(NASM) -dISFAT12 $(NASMBOOTFLAGS) boot.asm -l$*.lst -ofat12com.bin
 
 fat16com.bin:    boot.asm
-		$(NASM) -dISFAT16 boot.asm -l$*.lst -ofat16com.bin
+		$(NASM) -dISFAT16 $(NASMBOOTFLAGS) boot.asm -l$*.lst -ofat16com.bin
 
 fat32chs.bin:    boot32.asm
-		$(NASM) boot32.asm -l$*.lst -ofat32chs.bin
+		$(NASM) $(NASMBOOTFLAGS) boot32.asm -l$*.lst -ofat32chs.bin
 
 fat32lba.bin:    boot32lb.asm
-		$(NASM) boot32lb.asm -l$*.lst -ofat32lba.bin
+		$(NASM) $(NASMBOOTFLAGS) boot32lb.asm -l$*.lst -ofat32lba.bin
 
 oemfat12.bin:   oemboot.asm
-		$(NASM) -dISFAT12 oemboot.asm -l$*.lst -ooemfat12.bin
+		$(NASM) -dISFAT12 $(NASMBOOTFLAGS) oemboot.asm -l$*.lst -ooemfat12.bin
 
 oemfat16.bin:   oemboot.asm
-		$(NASM) -dISFAT16 oemboot.asm -l$*.lst -ooemfat16.bin
+		$(NASM) -dISFAT16 $(NASMBOOTFLAGS) oemboot.asm -l$*.lst -ooemfat16.bin
 
 clobber:        clean
 		-$(RM) *.bin status.me
diff --git a/build.bat b/build.bat
index 6e18b32..c0a627a 100644
--- a/build.bat
+++ b/build.bat
@@ -163,6 +163,8 @@ if "%1" == "" goto abort
 if "%2" == "/V" goto :setDefineWithValue
 set ALLCFLAGS=%ALLCFLAGS% -D%1
 set NASMFLAGS=%NASMFLAGS% -D%1
+REM $(NASMBOOTFLAGS) are extra flags only used when building boot sectors
+set NASMBOOTFLAGS=%NASMBOOTFLAGS% -d%1
 goto nextOption
 
 :setDefineWithValue
diff --git a/default.bat b/default.bat
index 3c5b487..5f24f02 100644
--- a/default.bat
+++ b/default.bat
@@ -80,6 +80,7 @@ set BC5_BASE=
 set MS_BASE=
 set XNASM=
 set NASMFLAGS=
+set NASMBOOTFLAGS=
 set XUPX=
 set UPXOPT=
 set LOADSEG=