diff --git a/rtl/msdos/prt0.asm b/rtl/msdos/prt0.asm
index 543ef73737..550c0d98e9 100644
--- a/rtl/msdos/prt0.asm
+++ b/rtl/msdos/prt0.asm
@@ -14,6 +14,10 @@
 	mov es, ax
 	jmp PASCALMAIN
 
+        global FPC_MSDOS
+FPC_MSDOS:
+        mov dx, ax
+        mov al, 21h
 	global FPC_INTR
 FPC_INTR:
 	mov byte [cs:int_number], al
diff --git a/rtl/msdos/system.pp b/rtl/msdos/system.pp
index 2a131a6742..b731c21461 100644
--- a/rtl/msdos/system.pp
+++ b/rtl/msdos/system.pp
@@ -66,11 +66,7 @@ implementation
 {$I registers.inc}
 
 procedure Intr(IntNo: Byte; var Regs: Registers); external name 'FPC_INTR';
-
-procedure MsDos(var Regs: Registers);
-begin
-  Intr($21, Regs);
-end;
+procedure MsDos(var Regs: Registers); external name 'FPC_MSDOS';
 
 {$I system.inc}