diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5dfc8989f..acecb01a3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -343,7 +343,7 @@ ENDIF("${CMAKE_SOURCE_DIR}" STREQUAL "${CMAKE_BINARY_DIR}")
 ################################################################################
 # Installation stuff
 
-SET(CMAKE_DEBUG_POSTFIX  "d")
+SET(CMAKE_DEBUG_POSTFIX "d" CACHE STRING "add a postfix, usually d on windows")
 
 IF(UNIX AND NOT WIN32 AND NOT APPLE)
   IF(CMAKE_SIZEOF_VOID_P MATCHES "8")