diff --git a/Source/CPack/cmCPackDocumentVariables.cxx b/Source/CPack/cmCPackDocumentVariables.cxx
index 6327152b5..68cde78d1 100644
--- a/Source/CPack/cmCPackDocumentVariables.cxx
+++ b/Source/CPack/cmCPackDocumentVariables.cxx
@@ -1,17 +1,25 @@
 #include "cmCPackDocumentVariables.h"
 #include "cmake.h"
 
-void cmCPackDocumentVariables::DefineVariables(cmake* )
+void cmCPackDocumentVariables::DefineVariables(cmake* cm)
 {
   // Subsection: variables defined/used by cpack,
   // which are common to all CPack generators
 
-//  cm->DefineProperty
-//      ("CPACK_PACKAGE_VENDOR", cmProperty::VARIABLE,
-//       "The name of the package vendor.",
-//       "If not specified, defaults to \"Humanity\"."
-//       "", false,
-//       "Variables common to all CPack generators");
+  cm->DefineProperty
+      ("CPACK_PACKAGING_INSTALL_PREFIX", cmProperty::VARIABLE,
+       "The prefix used in the built package.",
+       "Each CPack generator has a default value (like /usr)."
+       " This default value may"
+       " be overwritten from the CMakeLists.txt or the cpack command line"
+       " by setting an alternative value.\n"
+       "e.g. "
+       " set(CPACK_PACKAGING_INSTALL_PREFIX \"/opt\")\n"
+       "This is not the same purpose as CMAKE_INSTALL_PREFIX which"
+       " is used when installing from the build tree without building"
+       " a package."
+       "", false,
+       "Variables common to all CPack generators");
 
   // Subsection: variables defined/used by cpack,
   // which are specific to one CPack generator