diff --git a/plat/msdos386/boot.s b/plat/msdos386/boot.s
index 282dcb866..b30b6594c 100644
--- a/plat/msdos386/boot.s
+++ b/plat/msdos386/boot.s
@@ -36,7 +36,7 @@ begtext:
     cseg mov (interrupt_ptr+0), esi
     cseg o16 mov (transfer_buffer_ptr), di
 
-    mov eax, endbss
+    mov eax, __end
     cseg callf (realloc_ptr)
 
     ! Clear BSS.
@@ -161,7 +161,7 @@ empty_environment:
     add esp, 5*4
 
     ! Bail out if something went wrong.
-    test ax, ax
+    test eax, eax
     jnz no_room
 
     ! argc, argv, and envp are now at the stack top.  Now go.
@@ -197,6 +197,7 @@ rmode:               .space 2
 pmode_cs:            .space 2
 pmode_ds:            .space 2
 
+.define realloc_ptr
 .define interrupt_ptr
 .define rmode
 .define pmode_cs
diff --git a/plat/msdos386/libsys/brk.s b/plat/msdos386/libsys/brk.s
new file mode 100644
index 000000000..0e3170467
--- /dev/null
+++ b/plat/msdos386/libsys/brk.s
@@ -0,0 +1,23 @@
+! Declare segments (the order is important).
+
+.sect .text
+.sect .rom
+.sect .data
+.sect .bss
+
+.sect .text
+
+.extern realloc_ptr
+
+.define _brk
+_brk:
+	enter 0, 0
+newsize = 2*4
+
+	mov eax, newsize(ebp)
+	callf (realloc_ptr)
+	xor eax, eax
+	leave
+	ret
+
+
diff --git a/plat/msdos386/libsys/build.lua b/plat/msdos386/libsys/build.lua
index 4d349eb0f..71ac521b8 100644
--- a/plat/msdos386/libsys/build.lua
+++ b/plat/msdos386/libsys/build.lua
@@ -1,13 +1,14 @@
 acklibrary {
     name = "lib",
     srcs = {
-		"./brk.c",
+		"./_hol0.s",
+		"./brk.s",
 		"./close.s",
 		"./errno.s",
 		"./getpid.s",
-		"./_hol0.s",
 		"./isatty.s",
 		"./rename.s",
+		"./sbrk.c",
 		"./sys_exists.s",
 		"./sys_getdate.s",
 		"./sys_gettime.s",
diff --git a/plat/msdos386/libsys/brk.c b/plat/msdos386/libsys/sbrk.c
similarity index 61%
rename from plat/msdos386/libsys/brk.c
rename to plat/msdos386/libsys/sbrk.c
index ab333e550..988d406f3 100644
--- a/plat/msdos386/libsys/brk.c
+++ b/plat/msdos386/libsys/sbrk.c
@@ -8,29 +8,9 @@
 #include <unistd.h>
 #include "libsys.h"
 
-#define STACK_BUFFER 128 /* number of bytes to leave for stack */
-
 extern char _end[1];
 static char* current = _end;
 
-int brk(void* newend)
-{
-	/* This variable is used to figure out the current stack pointer,
-	 * by taking its address. */
-	char dummy;
-	char* p = newend;
-	
-	if ((p > (&dummy - STACK_BUFFER)) ||
-	    (p < _end))	
-	{
-		errno = ENOMEM;
-		return -1;
-	}
-		
-	current = p;
-	return 0;
-}
-
 void* sbrk(int increment)
 {
 	char* old;
diff --git a/plat/msdos386/libsys/sys_isreadyr.s b/plat/msdos386/libsys/sys_isreadyr.s
index 9a400859d..ff3960b27 100644
--- a/plat/msdos386/libsys/sys_isreadyr.s
+++ b/plat/msdos386/libsys/sys_isreadyr.s
@@ -17,13 +17,13 @@
 
 .define __sys_isreadyr
 __sys_isreadyr:
-	int 3
-	mov bx, sp
-	mov ax, 0x4406
-	mov bx, 2(bx)
+	mov ebx, sp
+	mov eax, 0x4406
+	mov ebx, 4(ebx)
 	int 0x21
 	jnc ok
 	movb al, 0
 ok:
 	cbw
+	cwd
 	ret
diff --git a/plat/msdos386/libsys/sys_rawread.s b/plat/msdos386/libsys/sys_rawread.s
index d7c14aa54..c8ba4bea0 100644
--- a/plat/msdos386/libsys/sys_rawread.s
+++ b/plat/msdos386/libsys/sys_rawread.s
@@ -26,5 +26,60 @@
 
 .define __sys_rawread
 __sys_rawread:
-	int 3
+	enter 4, 0
+amount_transferred = -1*4
+file_handle = 2*4
+write_buffer = 3*4
+amount_to_read = 4*4
+
+	mov amount_transferred(ebp), 0
+
+mainloop:
+	mov eax, amount_to_read(ebp)
+	test eax, eax
+	jz exit
+
+	mov ecx, 32*1024
+	cmp eax, ecx
+	jge 2f
+	mov ecx, eax
+2:
+
+	! Read from DOS into the transfer buffer.
+
+	movb ah, 0x3f
+	o16 mov dx, (transfer_buffer_ptr)
+	o16 mov bx, file_handle(ebp)
+	mov ecx, 0x80
+	or ebx, 0x210000
+	callf (interrupt_ptr)
+	jc exit
+	test eax, eax
+	jz exit
+
+	! Copy eax bytes out of the transfer buffer.
+
+	mov ecx, eax
+	push eax
+	movzx esi, (transfer_buffer_ptr)
+	mov edi, write_buffer(ebp)
+	mov es, (pmode_ds)
+	cld
+1:
+	eseg lods
+	movb (edi), al
+	add edi, 4
+	loop 1b
+	pop eax
+
+	add write_buffer(ebp), eax
+	add amount_transferred(ebp), eax
+	sub amount_to_read(ebp), eax
+	jmp mainloop
+
+exit:
+	mov eax, amount_transferred(ebp)
+	leave
+	ret
+
 
diff --git a/plat/msdos386/libsys/sys_rawwrite.s b/plat/msdos386/libsys/sys_rawwrite.s
index e13e5e52c..bef6481b2 100644
--- a/plat/msdos386/libsys/sys_rawwrite.s
+++ b/plat/msdos386/libsys/sys_rawwrite.s
@@ -32,31 +32,39 @@ file_handle = 2*4
 read_buffer = 3*4
 amount_to_write = 4*4
 
-	mov es, (pmode_ds)
 	mov amount_transferred(ebp), 0
 
 mainloop:
-	mov ecx, 32*1024
-	cmp amount_to_write(ebp), ecx
-	jge 2f
-	mov ecx, amount_to_write(ebp)
-	test ecx, ecx
+	mov eax, amount_to_write(ebp)
+	test eax, eax
 	jz exit
+
+	mov ecx, 32*1024
+	cmp eax, ecx
+	jge 2f
+	mov ecx, eax
 2:
+
 	! Copy ecx bytes into the transfer buffer.
 
 	push ecx
 	mov esi, read_buffer(ebp)
 	movzx edi, (transfer_buffer_ptr)
+	mov es, (pmode_ds)
+	cld
 	rep movsb
 	pop ecx
 
+	! Write from the transfer buffer to DOS.
+
 	movb ah, 0x40
 	o16 mov dx, (transfer_buffer_ptr)
 	o16 mov bx, file_handle(ebp)
 	or ebx, 0x210000
 	callf (interrupt_ptr)
-	movzx eax, ax
+	jc exit
+
+	! Update counters and go again.
 
 	add read_buffer(ebp), eax
 	add amount_transferred(ebp), eax
@@ -64,7 +72,7 @@ mainloop:
 	jmp mainloop
 
 exit:
-	mov eax, amount_to_write(ebp)
+	mov eax, amount_transferred(ebp)
 	leave
 	ret
 
diff --git a/plat/msdos386/stub.s b/plat/msdos386/stub.s
index 03887ec5d..725d3431e 100644
--- a/plat/msdos386/stub.s
+++ b/plat/msdos386/stub.s
@@ -337,12 +337,12 @@ interrupt:
     pop ds
     pop es
     pushf
-    mov ax, (dpmi_eax)
-    mov bx, (dpmi_ebx)
-    mov cx, (dpmi_ecx)
-    mov dx, (dpmi_edx)
-    mov si, (dpmi_esi)
-    mov di, (dpmi_edi)
+    o32 movzx eax, (dpmi_eax)
+    o32 movzx ebx, (dpmi_ebx)
+    o32 movzx ecx, (dpmi_ecx)
+    o32 movzx edx, (dpmi_edx)
+    o32 movzx esi, (dpmi_esi)
+    o32 movzx edi, (dpmi_edi)
     popf
     ret