Index: /trunk/src/VBox/Additions/WINNT/Installer/VBoxGuestAdditions.nsi
===================================================================
--- /trunk/src/VBox/Additions/WINNT/Installer/VBoxGuestAdditions.nsi	(revision 46844)
+++ /trunk/src/VBox/Additions/WINNT/Installer/VBoxGuestAdditions.nsi	(revision 46845)
@@ -761,4 +761,5 @@
   ${OrIf} $R0 == '7'     ; Windows 7.
   ${OrIf} $R0 == '8'     ; Windows 8.
+  ${OrIf} $R0 == '8_1'   ; Windows 8.1 / Windows Server 2012 R2.
     ; Use VBoxCredProv on Vista and up.
     ${LogVerbose} "Installing VirtualBox credential provider ..."
@@ -1069,5 +1070,6 @@
   ${Else} ; D3D unselected again
 
-    ${If} $g_strWinVersion != "8" ; On Windows 8 WDDM is mandatory
+    ${If}   $g_strWinVersion != "8"   ; On Windows 8 WDDM is mandatory
+    ${OrIf} $g_strWinVersion != "8_1" ; ... also on Windows 8.1 / Windows 2012 Server R2
       StrCpy $g_bWithWDDM "false"
     ${EndIf}
@@ -1248,7 +1250,8 @@
     !insertmacro SelectSection ${SEC03}
   ${EndIf}
-  ; On Windows 8 we always select the 3D section and
-  ; disable it so that it cannot be deselected again
-  ${If} $g_strWinVersion == "8"
+  ; On Windows 8 / 8.1 / Windows Server 2012 R2 we always select the 3D 
+  ; section and disable it so that it cannot be deselected again
+  ${If}   $g_strWinVersion == "8"
+  ${OrIf} $g_strWinVersion == "8_1"
     IntOp $0 ${SF_SELECTED} | ${SF_RO}
     SectionSetFlags ${SEC03} $0
Index: /trunk/src/VBox/Additions/WINNT/Installer/VBoxGuestAdditionsCommon.nsh
===================================================================
--- /trunk/src/VBox/Additions/WINNT/Installer/VBoxGuestAdditionsCommon.nsh	(revision 46844)
+++ /trunk/src/VBox/Additions/WINNT/Installer/VBoxGuestAdditionsCommon.nsh	(revision 46845)
@@ -541,7 +541,8 @@
 !if $%VBOX_WITH_WDDM% == "1"
   ; If we're on a 32-bit Windows Vista / 7 / 8 we can use the WDDM driver
-  ${If} $g_strWinVersion == "Vista"
+  ${If}   $g_strWinVersion == "Vista"
   ${OrIf} $g_strWinVersion == "7"
   ${OrIf} $g_strWinVersion == "8"
+  ${OrIf} $g_strWinVersion == "8_1"
     StrCpy $g_bCapWDDM "true"
     ${LogVerbose} "OS is WDDM driver capable"
@@ -549,5 +550,6 @@
   ; If we're on Windows 8 we *have* to use the WDDM driver, so select it
   ; by default
-  ${If} $g_strWinVersion == "8"
+  ${If}   $g_strWinVersion == "8"
+  ${OrIf} $g_strWinVersion == "8_1"
     StrCpy $g_bWithWDDM "true"
     ${LogVerbose} "OS needs WDDM driver by default"
@@ -570,7 +572,8 @@
 
   ; Does the guest have a DLL cache?
-  ${If} $g_strWinVersion == "Vista"
+  ${If}   $g_strWinVersion == "Vista"
   ${OrIf} $g_strWinVersion == "7"
   ${OrIf} $g_strWinVersion == "8"
+  ${OrIf} $g_strWinVersion == "8_1"
     StrCpy $g_bCapDllCache "true"
     ${LogVerbose}  "OS has a DLL cache"
Index: /trunk/src/VBox/Additions/WINNT/Installer/VBoxGuestAdditionsUninstall.nsh
===================================================================
--- /trunk/src/VBox/Additions/WINNT/Installer/VBoxGuestAdditionsUninstall.nsh	(revision 46844)
+++ /trunk/src/VBox/Additions/WINNT/Installer/VBoxGuestAdditionsUninstall.nsh	(revision 46845)
@@ -86,4 +86,5 @@
   StrCmp $g_strWinVersion "7" vista     ; Windows 7
   StrCmp $g_strWinVersion "8" vista     ; Windows 8
+  StrCmp $g_strWinVersion "8_1" vista   ; Windows 8.1 / Windows Server 2012 R2
 
   ${If} $g_bForceInstall == "true"
@@ -144,4 +145,5 @@
   StrCmp $g_strWinVersion "7" vista     ; Windows 7
   StrCmp $g_strWinVersion "8" vista     ; Windows 8
+  StrCmp $g_strWinVersion "8_1" vista   ; Windows 8.1 / Windows Server 2012 R2
 
   ${If} $g_bForceInstall == "true"
Index: /trunk/src/VBox/Additions/WINNT/Installer/VBoxGuestAdditionsW2KXP.nsh
===================================================================
--- /trunk/src/VBox/Additions/WINNT/Installer/VBoxGuestAdditionsW2KXP.nsh	(revision 46844)
+++ /trunk/src/VBox/Additions/WINNT/Installer/VBoxGuestAdditionsW2KXP.nsh	(revision 46845)
@@ -121,4 +121,5 @@
   ${OrIf} $g_strWinVersion == "7"
   ${OrIf} $g_strWinVersion == "8"
+  ${OrIf} $g_strWinVersion == "8_1"
     StrCpy $reg_path_device "SYSTEM\CurrentControlSet\Control\Video\$dev_id\0000"
     StrCpy $reg_path_monitor "SYSTEM\CurrentControlSet\Control\VIDEO\$dev_id\0000\Mon00000001"