diff --git a/library.cmake b/library.cmake
index 8e07552..627dcb7 100644
--- a/library.cmake
+++ b/library.cmake
@@ -12,7 +12,7 @@ if (${PROJECT_NAME}_CURRENT_BINARY_DIR)
 endif()
 message(STATUS "CURRENT_PROJECT_BINARY_DIR : ${CURRENT_PROJECT_BINARY_DIR}")
 
-if(DEFINED ${BUILD_STATIC})
+if( ${BUILD_STATIC} )
     if(${BUILD_STATIC} STREQUAL "ON")
         set(SHARED_OR_STATIC "STATIC")
     else()