diff --git a/src/bin/writembr/Jamfile b/src/bin/writembr/Jamfile
index 2674876573..6c33228b4f 100644
--- a/src/bin/writembr/Jamfile
+++ b/src/bin/writembr/Jamfile
@@ -10,7 +10,7 @@ Application writembr :
 
 # Assemble the MBR code, and convert it into a header file
 
-NASMFLAGS on [ FGristFiles mbr.bin ] = -f bin -O5 -dMBR_CODE_ONLY=1 ;
+NASMFLAGS on [ FGristFiles mbr.bin ] = -f bin -O5 ;
 
 Object [ FGristFiles mbr.bin ] : mbr.nasm ;
 
diff --git a/src/bin/writembr/mbr.nasm b/src/bin/writembr/mbr.nasm
index 0aab120516..64bad167ef 100644
--- a/src/bin/writembr/mbr.nasm
+++ b/src/bin/writembr/mbr.nasm
@@ -218,7 +218,7 @@ found_active:								; active partition (pointed by si)
 		mov [address_packet+AddressPacket.sector],eax
 
 		; if LBA_adress equals 0 then it's not a valid PBR (it is the MBR)
-		; this can append when we only have a CHS adress in the partition entry
+		; this can happen when we only have a CHS adress in the partition entry
 		test	eax,		eax				;if ( LBA_adress == 0 )
 		jz		no_disk_extentions			;then no_disk_extentions()
 
diff --git a/src/bin/writembr/writembr.cpp b/src/bin/writembr/writembr.cpp
index 5526b0f6da..1661683729 100644
--- a/src/bin/writembr/writembr.cpp
+++ b/src/bin/writembr/writembr.cpp
@@ -9,6 +9,7 @@
 #include <string.h>
 #include <string>
 
+#include <Debug.h>
 #include <DiskDevice.h>
 #include <DiskDeviceRoster.h>
 #include <Path.h>
@@ -73,6 +74,8 @@ main(int argc, char** argv)
 		return B_ERROR;
 	}
 
+	STATIC_ASSERT(kMBRSize == 512);
+
 	unsigned char MBR[kMBRSize];
 	fs.read((char*)MBR, kMBRSize);
 	if (fs.fail() || fs.gcount() < kMBRSize ) {