diff --git a/CMakeLists.txt b/CMakeLists.txt
index 11887ad..ae775c4 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -186,7 +186,7 @@ if(NOT CMAKE_INSTALL_PREFIX)
 endif(NOT CMAKE_INSTALL_PREFIX)
 
 # Check if it is a 64 bit system
-if(CMAKE_SIZEOF_VOID_P EQUAL 8 AND NOT LIB_SUFFIX)
+if(CMAKE_SIZEOF_VOID_P EQUAL 8 AND NOT DEFINED LIB_SUFFIX)
     set(LIB_SUFFIX "64")
 endif()