diff --git a/LICENSE.TXT b/LICENSE.TXT
index 2b2fc7b..f4778b3 100644
--- a/LICENSE.TXT
+++ b/LICENSE.TXT
@@ -1,5 +1,5 @@
 
-flat assembler  version 1.72
+flat assembler  version 1.73
 Copyright (c) 1999-2017, Tomasz Grysztar.
 All rights reserved.
 
diff --git a/SOURCE/ASSEMBLE.INC b/SOURCE/ASSEMBLE.INC
index 8b028ff..6112808 100644
--- a/SOURCE/ASSEMBLE.INC
+++ b/SOURCE/ASSEMBLE.INC
@@ -148,8 +148,8 @@ create_addressing_space:
       init_addressing_space:
 	mov	ebx,[tagged_blocks]
 	mov	dword [ebx-4],10h
-	mov	dword [ebx-8],20h
-	sub	ebx,8+20h
+	mov	dword [ebx-8],24h
+	sub	ebx,8+24h
 	cmp	ebx,edi
 	jbe	out_of_memory
 	mov	[tagged_blocks],ebx
@@ -162,6 +162,7 @@ create_addressing_space:
 	mov	[ebx+14h],eax
 	mov	[ebx+18h],edi
 	mov	[ebx+1Ch],eax
+	mov	[ebx+20h],eax
 	ret
 
 assemble_line:
@@ -780,6 +781,8 @@ show_display_buffer:
 	mov	eax,[esi+4]
 	mov	ecx,[esi]
 	sub	esi,ecx
+	cmp	eax,10h
+	je	write_addressing_space
 	test	eax,eax
 	jnz	skip_block
 	push	esi
@@ -790,6 +793,62 @@ show_display_buffer:
 	jne	display_messages
       display_done:
 	ret
+      write_addressing_space:
+	mov	ecx,[esi+20h]
+	jecxz	skip_block
+	push	esi
+	mov	edi,[free_additional_memory]
+	mov	esi,[output_file]
+	test	esi,esi
+	jz	addressing_space_written
+	xor	ebx,ebx
+      copy_output_path:
+	lodsb
+	cmp	edi,[structures_buffer]
+	jae	out_of_memory
+	stosb
+	test	al,al
+	jz	output_path_copied
+	cmp	al,'/'
+	je	new_path_segment
+	cmp	al,'\'
+	je	new_path_segment
+	cmp	al,'.'
+	jne	copy_output_path
+	mov	ebx,edi
+	jmp	copy_output_path
+      new_path_segment:
+	xor	ebx,ebx
+	jmp	copy_output_path
+      output_path_copied:
+	test	ebx,ebx
+	jnz	append_extension
+	mov	byte [edi-1],'.'
+	mov	ebx,edi
+      append_extension:
+	mov	edi,ebx
+	add	ebx,ecx
+	inc	ebx
+	cmp	ebx,[structures_buffer]
+	jae	out_of_memory
+	mov	esi,[esp]
+	mov	esi,[esi+18h]
+	sub	esi,ecx
+	rep	movs byte [edi],[esi]
+	xor	al,al
+	stos	byte [edi]
+	mov	edx,[free_additional_memory]
+	call	create
+	jc	write_failed
+	mov	esi,[esp]
+	mov	edx,[esi+18h]
+	mov	ecx,[esi+1Ch]
+	call	write
+	jc	write_failed
+	call	close
+      addressing_space_written:
+	pop	esi
+	jmp	skip_block
 
 times_directive:
 	lods	byte [esi]
@@ -882,6 +941,24 @@ virtual_directive:
 	mov	[ebx+1Ch],eax
 	call	init_addressing_space
 	or	byte [ebx+0Ah],1
+	cmp	byte [esi],86h
+	jne	addressing_space_extension_ok
+	cmp	word [esi+1],'('
+	jne	invalid_argument
+	mov	ecx,[esi+3]
+	add	esi,3+4
+	add	[ebx+18h],ecx
+	mov	[ebx+20h],ecx
+	mov	ebx,characters
+      get_extension:
+	lods	byte [esi]
+	stos	byte [edi]
+	xlat	byte [ebx]
+	test	al,al
+	jz	invalid_argument
+	loop	get_extension
+	inc	esi
+      addressing_space_extension_ok:
 	pop	eax
 	mov	cl,[address_sign]
 	not	eax
@@ -951,6 +1028,7 @@ virtual_directive:
 	mov	eax,edi
 	sub	eax,[ebx+18h]
 	mov	[ebx+1Ch],eax
+	add	eax,[ebx+20h]
 	test	byte [ebx+0Ah],2
 	jz	addressing_space_closed
 	push	esi edi ecx edx
@@ -962,7 +1040,9 @@ virtual_directive:
 	sub	eax,ecx
 	mov	[tagged_blocks],eax
 	lea	edi,[eax+ecx-1]
+	add	eax,[ebx+20h]
 	xchg	eax,[ebx+18h]
+	sub	eax,[ebx+20h]
 	lea	esi,[eax+ecx-1]
 	mov	eax,edi
 	sub	eax,esi
diff --git a/SOURCE/DOS/SYSTEM.INC b/SOURCE/DOS/SYSTEM.INC
index fe616a3..474f14a 100644
--- a/SOURCE/DOS/SYSTEM.INC
+++ b/SOURCE/DOS/SYSTEM.INC
@@ -334,6 +334,7 @@ fatal_error:
 	mov	al,0FFh
 	jmp	exit_program
 assembler_error:
+	and	[output_file],0
 	call	display_user_messages
 	mov	ebx,[current_line]
 	test	ebx,ebx
diff --git a/SOURCE/FORMATS.INC b/SOURCE/FORMATS.INC
index e92f80f..179e7c4 100644
--- a/SOURCE/FORMATS.INC
+++ b/SOURCE/FORMATS.INC
@@ -9,13 +9,13 @@ formatter:
 	jne	output_path_ok
 	mov	esi,[input_file]
 	mov	edi,[free_additional_memory]
-      copy_output_path:
+      duplicate_output_path:
 	lods	byte [esi]
 	cmp	edi,[structures_buffer]
 	jae	out_of_memory
 	stos	byte [edi]
 	or	al,al
-	jnz	copy_output_path
+	jnz	duplicate_output_path
 	dec	edi
 	mov	eax,edi
       find_extension:
diff --git a/SOURCE/LIBC/SYSTEM.INC b/SOURCE/LIBC/SYSTEM.INC
index f16f92a..4f64666 100644
--- a/SOURCE/LIBC/SYSTEM.INC
+++ b/SOURCE/LIBC/SYSTEM.INC
@@ -131,16 +131,9 @@ lseek:
 	push	ebx
 	movzx	eax,al
 	ccall	fseek,ebx,edx,eax
-	test	eax,eax
-	jnz	lseek_error
 	mov	ebx,[esp]
 	ccall	ftell,ebx
 	pop	ebx
-	clc
-	ret
-    lseek_error:
-	pop	ebx
-	stc
 	ret
 
 display_string:
@@ -227,6 +220,7 @@ fatal_error:
 	jmp	exit_program
 assembler_error:
 	mov	[con_handle],2
+	and	[output_file],0
 	call	display_user_messages
 	mov	ebx,[current_line]
 	test	ebx,ebx
diff --git a/SOURCE/LINUX/SYSTEM.INC b/SOURCE/LINUX/SYSTEM.INC
index eec75fd..53cba01 100644
--- a/SOURCE/LINUX/SYSTEM.INC
+++ b/SOURCE/LINUX/SYSTEM.INC
@@ -186,9 +186,6 @@ lseek:
 	mov	dl,al
 	mov	eax,19
 	int	0x80
-	cmp	eax,-1
-	je	file_error
-	clc
 	ret
 
 display_string:
@@ -287,6 +284,7 @@ fatal_error:
 	jmp	exit_program
 assembler_error:
 	mov	[con_handle],2
+	and	[output_file],0
 	call	display_user_messages
 	mov	ebx,[current_line]
 	test	ebx,ebx
diff --git a/SOURCE/LINUX/X64/SYSTEM.INC b/SOURCE/LINUX/X64/SYSTEM.INC
index fe7b60d..1344afc 100644
--- a/SOURCE/LINUX/X64/SYSTEM.INC
+++ b/SOURCE/LINUX/X64/SYSTEM.INC
@@ -220,9 +220,6 @@ lseek:
 	syscall
 	mov	esi,r12d
 	mov	edi,r13d
-	cmp	eax,-1
-	je	file_error
-	clc
 	ret
 
 display_string:
@@ -321,6 +318,7 @@ fatal_error:
 	jmp	exit_program
 assembler_error:
 	mov	[con_handle],2
+	and	[output_file],0
 	call	display_user_messages
 	mov	ebx,[current_line]
 	test	ebx,ebx
diff --git a/SOURCE/VERSION.INC b/SOURCE/VERSION.INC
index 5028e29..fa763f7 100644
--- a/SOURCE/VERSION.INC
+++ b/SOURCE/VERSION.INC
@@ -1,5 +1,5 @@
 
-; flat assembler  version 1.72
+; flat assembler  version 1.73
 ; Copyright (c) 1999-2017, Tomasz Grysztar.
 ; All rights reserved.
 ;
@@ -33,7 +33,7 @@
 ; cannot simply be copied and put under another distribution licence
 ; (including the GNU Public Licence).
 
-VERSION_STRING equ "1.72"
+VERSION_STRING equ "1.73.00"
 
 VERSION_MAJOR = 1
-VERSION_MINOR = 72
+VERSION_MINOR = 73
diff --git a/SOURCE/WIN32/SYSTEM.INC b/SOURCE/WIN32/SYSTEM.INC
index 6d519c0..04849cb 100644
--- a/SOURCE/WIN32/SYSTEM.INC
+++ b/SOURCE/WIN32/SYSTEM.INC
@@ -187,9 +187,6 @@ lseek:
 	push	edx
 	push	ebx
 	call	[SetFilePointer]
-	cmp	eax,-1
-	je	file_error
-	clc
 	ret
 
 display_string:
@@ -317,6 +314,7 @@ fatal_error:
 	jmp	exit_program
 assembler_error:
 	mov	[con_handle],STD_ERROR_HANDLE
+	and	[output_file],0
 	call	display_user_messages
 	mov	ebx,[current_line]
 	test	ebx,ebx
diff --git a/WHATSNEW.TXT b/WHATSNEW.TXT
index 1dfca61..a91e937 100644
--- a/WHATSNEW.TXT
+++ b/WHATSNEW.TXT
@@ -2,6 +2,11 @@
 Visit http://flatassembler.net/ for more information.
 
 
+version 1.73.00 (Nov 24, 2017)
+
+[+] Added "virtual as" syntax (backported from flat assembler g).
+
+
 version 1.72 (Oct 10, 2017)
 
 [+] Support for Intel AVX-512, SHA, CLFLUSHOPT, CLWB, PCOMMIT, ADX, RDSEED, SMAP