diff --git a/Modules/NSIS.template.in b/Modules/NSIS.template.in
index 776bc07..e4a2336 100644
--- a/Modules/NSIS.template.in
+++ b/Modules/NSIS.template.in
@@ -898,6 +898,27 @@ SectionEnd
 ; "Program Files" for AllUsers, "My Documents" for JustMe...
 
 Function .onInit
+
+  ReadRegStr $0 HKLM "Software\Microsoft\Windows\CurrentVersion\Uninstall\@CPACK_PACKAGE_NAME@" "UninstallString"
+  StrCmp $0 "" inst
+
+  MessageBox MB_YESNOCANCEL|MB_ICONEXCLAMATION \
+  "@CPACK_NSIS_PACKAGE_NAME@ is already installed. $\n$\nDo you want to uninstall the old version before installing the new one." \
+  IDYES uninst IDNO inst
+  Abort
+
+;Run the uninstaller
+uninst:
+  ClearErrors
+  ExecWait '$0 _?=$INSTDIR' ;Do not copy the uninstaller to a temp file
+ 
+  IfErrors uninst_failed inst
+uninst_failed:
+  MessageBox MB_OK|MB_ICONSTOP "Uninstall failed."
+  Abort
+
+
+inst:
   ; Reads components status for registry
   !insertmacro SectionList "InitSection"
 

From 512a85653e13f4d10501d5e6264535c61cad6bab Mon Sep 17 00:00:00 2001
From: Patrick Gansterer <paroga@paroga.com>
Date: Sat, 11 Jun 2011 11:54:19 +0200
Subject: [PATCH] Added CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL

If CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL is set to ON the NSIS installer will look for a previous installed version and ask the user about uninstall.
---
 Modules/CPack.cmake      |    4 ++++
 Modules/NSIS.template.in |   22 ++++++++++++++++++++++
 2 files changed, 26 insertions(+), 0 deletions(-)

diff --git a/Modules/CPack.cmake b/Modules/CPack.cmake
index bf52b25..1e8f9c6 100644
--- a/Modules/CPack.cmake
+++ b/Modules/CPack.cmake
@@ -297,6 +297,10 @@ cpack_set_if_not_set(CPACK_RESOURCE_FILE_WELCOME
 
 cpack_set_if_not_set(CPACK_MODULE_PATH "${CMAKE_MODULE_PATH}")
 
+IF(CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL)
+  SET(CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL ON)
+ENDIF(CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL)
+
 IF(CPACK_NSIS_MODIFY_PATH)
   SET(CPACK_NSIS_MODIFY_PATH ON)
 ENDIF(CPACK_NSIS_MODIFY_PATH)
diff --git a/Modules/NSIS.template.in b/Modules/NSIS.template.in
index df9d2d3..0ee6272 100644
--- a/Modules/NSIS.template.in
+++ b/Modules/NSIS.template.in
@@ -899,6 +899,28 @@ SectionEnd
 ; "Program Files" for AllUsers, "My Documents" for JustMe...
 
 Function .onInit
+  StrCmp "@CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL@" "ON" 0 inst
+
+  ReadRegStr $0 HKLM "Software\Microsoft\Windows\CurrentVersion\Uninstall\@CPACK_PACKAGE_NAME@" "UninstallString"
+  StrCmp $0 "" inst
+
+  MessageBox MB_YESNOCANCEL|MB_ICONEXCLAMATION \
+  "@CPACK_NSIS_PACKAGE_NAME@ is already installed. $\n$\nDo you want to uninstall the old version before installing the new one?" \
+  IDYES uninst IDNO inst
+  Abort
+
+;Run the uninstaller
+uninst:
+  ClearErrors
+  ExecWait '$0 _?=$INSTDIR' ;Do not copy the uninstaller to a temp file
+
+  IfErrors uninst_failed inst
+uninst_failed:
+  MessageBox MB_OK|MB_ICONSTOP "Uninstall failed."
+  Abort
+
+
+inst:
   ; Reads components status for registry
   !insertmacro SectionList "InitSection"
 
-- 
1.7.4.msysgit.0

From 3c2929155fa6819327159b1082517dbfb9c23320 Mon Sep 17 00:00:00 2001
From: Patrick Gansterer <paroga@paroga.com>
Date: Sat, 11 Jun 2011 12:14:56 +0200
Subject: [PATCH] Added CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL

If CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL is set to ON the NSIS installer will look for a previous installed version and ask the user about uninstall.
---
 Modules/CPack.cmake      |    4 ++++
 Modules/CPackNSIS.cmake  |    4 ++++
 Modules/NSIS.template.in |   22 ++++++++++++++++++++++
 3 files changed, 30 insertions(+), 0 deletions(-)

diff --git a/Modules/CPack.cmake b/Modules/CPack.cmake
index bf52b25..1e8f9c6 100644
--- a/Modules/CPack.cmake
+++ b/Modules/CPack.cmake
@@ -297,6 +297,10 @@ cpack_set_if_not_set(CPACK_RESOURCE_FILE_WELCOME
 
 cpack_set_if_not_set(CPACK_MODULE_PATH "${CMAKE_MODULE_PATH}")
 
+IF(CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL)
+  SET(CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL ON)
+ENDIF(CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL)
+
 IF(CPACK_NSIS_MODIFY_PATH)
   SET(CPACK_NSIS_MODIFY_PATH ON)
 ENDIF(CPACK_NSIS_MODIFY_PATH)
diff --git a/Modules/CPackNSIS.cmake b/Modules/CPackNSIS.cmake
index d9dab53..e87358f 100644
--- a/Modules/CPackNSIS.cmake
+++ b/Modules/CPackNSIS.cmake
@@ -29,6 +29,10 @@
 #   CPACK_NSIS_COMPRESSOR - The arguments that will be passed to the
 #   NSIS SetCompressor command.
 #
+#   CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL - If this is set to "ON",
+#   then an the installer will look for previous installed versions and
+#   and ask the user about uninstall (if found) before install.
+#
 #   CPACK_NSIS_MODIFY_PATH - If this is set to "ON", then an extra page
 #   will appear in the installer that will allow the user to choose
 #   whether the program directory should be added to the system PATH
diff --git a/Modules/NSIS.template.in b/Modules/NSIS.template.in
index df9d2d3..0ee6272 100644
--- a/Modules/NSIS.template.in
+++ b/Modules/NSIS.template.in
@@ -899,6 +899,28 @@ SectionEnd
 ; "Program Files" for AllUsers, "My Documents" for JustMe...
 
 Function .onInit
+  StrCmp "@CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL@" "ON" 0 inst
+
+  ReadRegStr $0 HKLM "Software\Microsoft\Windows\CurrentVersion\Uninstall\@CPACK_PACKAGE_NAME@" "UninstallString"
+  StrCmp $0 "" inst
+
+  MessageBox MB_YESNOCANCEL|MB_ICONEXCLAMATION \
+  "@CPACK_NSIS_PACKAGE_NAME@ is already installed. $\n$\nDo you want to uninstall the old version before installing the new one?" \
+  IDYES uninst IDNO inst
+  Abort
+
+;Run the uninstaller
+uninst:
+  ClearErrors
+  ExecWait '$0 _?=$INSTDIR' ;Do not copy the uninstaller to a temp file
+
+  IfErrors uninst_failed inst
+uninst_failed:
+  MessageBox MB_OK|MB_ICONSTOP "Uninstall failed."
+  Abort
+
+
+inst:
   ; Reads components status for registry
   !insertmacro SectionList "InitSection"
 
-- 
1.7.4.msysgit.0