diff --git a/CMakeLists.txt b/CMakeLists.txt
index 33ee139cb..00ac11c20 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -103,7 +103,9 @@ if(UNIX OR MINGW)
         endif()
     endif()
 elseif(MSVC)
-    set(CMAKE_DEBUG_POSTFIX "d")
+    if(NOT DEFINED CMAKE_DEBUG_POSTFIX)
+        set(CMAKE_DEBUG_POSTFIX "d")
+    endif()
     add_definitions(-D_CRT_SECURE_NO_DEPRECATE)
     add_definitions(-D_CRT_NONSTDC_NO_DEPRECATE)