diff --git a/CMake/cmake/modules/OptionalAddSubdirectory.cmake b/CMake/cmake/modules/OptionalAddSubdirectory.cmake
index 0bb8860fa35..5ff142df744 100644
--- a/CMake/cmake/modules/OptionalAddSubdirectory.cmake
+++ b/CMake/cmake/modules/OptionalAddSubdirectory.cmake
@@ -11,8 +11,9 @@ endmacro()
 
 macro( optional_add_subdirectory dir def)
   set( WITH_${dir}_ENV $ENV{WITH_${dir}} )
-  if ( DEFINED WITH_${dir}_ENV )
-    set( WITH_${dir} ${WITH_${dir}_ENV} CACHE STRING "Select ${dir} package." FORCE )
+  if ( NOT ${WITH_${dir}_ENV} STREQUAL "" )
+    message ( STATUS "WITH_${dir}_ENV given as enviroment variable: ${WITH_${dir}_ENV}" )
+    set( WITH_${dir} ${WITH_${dir}_ENV} CACHE BOOL "Select ${dir} package." FORCE )
   endif()
   option( WITH_${dir} "Select ${dir} package." ${def} )
   add_subdirectory_if( WITH_${dir} ${dir} ${ARGN} )