diff --git a/Modules/CPack.cmake b/Modules/CPack.cmake
index 1b2fa616c..e5721192c 100644
--- a/Modules/CPack.cmake
+++ b/Modules/CPack.cmake
@@ -342,6 +342,10 @@ 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 66c33a8df..d14005369 100644
--- a/Modules/CPackNSIS.cmake
+++ b/Modules/CPackNSIS.cmake
@@ -54,6 +54,14 @@
 ##end
 #
 ##variable
+#   CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL - Ask about uninstalling
+#   previous versions first.
+#   If this is set to "ON", then an installer will look for previous
+#   installed versions and if one is found, ask the user whether to
+#   uninstall it before proceeding with the install.
+##end
+#
+##variable
 #   CPACK_NSIS_MODIFY_PATH - Modify PATH toggle.
 #   If this is set to "ON", then an extra page
 #   will appear in the installer that will allow the user to choose
diff --git a/Modules/NSIS.template.in b/Modules/NSIS.template.in
index e7edead2a..43f72f6aa 100644
--- a/Modules/NSIS.template.in
+++ b/Modules/NSIS.template.in
@@ -900,6 +900,28 @@ 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"