diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8372d6f4..56d358bf 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -3,7 +3,7 @@ cmake_minimum_required(VERSION 2.8)
 
 # define a macro that helps defining an option
 macro(sfml_set_option var default type docstring)
-    if(DEFINED ${var})
+    if(NOT DEFINED ${var})
         set(${var} ${default})
     endif()
     set(${var} ${${var}} CACHE ${type} ${docstring} FORCE)