Index: /trunk/src/VBox/Additions/WINNT/Installer/VBoxGuestAdditions.nsi
===================================================================
--- /trunk/src/VBox/Additions/WINNT/Installer/VBoxGuestAdditions.nsi	(revision 46837)
+++ /trunk/src/VBox/Additions/WINNT/Installer/VBoxGuestAdditions.nsi	(revision 46838)
@@ -654,4 +654,5 @@
 
   ; Which OS are we using?
+  ; @todo Use logic lib here
 !if $%BUILD_TARGET_ARCH% == "x86"       ; 32-bit
   StrCmp $g_strWinVersion "NT4" nt4     ; Windows NT 4.0
@@ -663,4 +664,5 @@
   StrCmp $g_strWinVersion "7" vista     ; Windows 7
   StrCmp $g_strWinVersion "8" vista     ; Windows 8
+  StrCmp $g_strWinVersion "8_1" vista   ; Windows 8.1 / Windows 2012 Server R2
 
   ${If} $g_bForceInstall == "true"
@@ -698,5 +700,5 @@
   goto success
 
-vista: ; Windows Vista / Windows 7 / Windows 8
+vista: ; Windows Vista / Windows 7 / Windows 8(.1)
 
   ; Check requirments; this function can abort the installation if necessary!
Index: /trunk/src/VBox/Additions/WINNT/Installer/winver.nsh
===================================================================
--- /trunk/src/VBox/Additions/WINNT/Installer/winver.nsh	(revision 46837)
+++ /trunk/src/VBox/Additions/WINNT/Installer/winver.nsh	(revision 46838)
@@ -66,5 +66,6 @@
   StrCmp $R1 '6.0' lbl_winnt_vista
   StrCmp $R1 '6.1' lbl_winnt_7
-  StrCmp $R1 '6.2' lbl_winnt_8 lbl_error
+  StrCmp $R1 '6.2' lbl_winnt_8
+  StrCmp $R1 '6.3' lbl_winnt_8_1 lbl_error
 
   lbl_winnt_x:
@@ -96,4 +97,8 @@
   Goto lbl_done
 
+  lbl_winnt_8_1: ; Also includes Windows Server 2012 R2
+    Strcpy $R0 '8_1'
+  Goto lbl_done
+
   lbl_error:
     Strcpy $R0 ''