diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3875b82..0cc28be 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -108,9 +108,11 @@ if(APPLE)
   endif()
   message(STATUS "EbsdLib: DARWIN_VERSION ${DARWIN_VERSION}")
   message(STATUS "EbsdLib: CMAKE_OSX_DEPLOYMENT_TARGET: ${CMAKE_OSX_DEPLOYMENT_TARGET}")
-  if(CMAKE_OSX_DEPLOYMENT_TARGET VERSION_LESS 10.15)
-    message(STATUS "EbsdLib: CMAKE_OSX_DEPLOYMENT_TARGET less than 10.15. Enabling EbsdLib_USE_GHC_FILESYSTEM")
-    set(EbsdLib_USE_GHC_FILESYSTEM ON)
+  if(NOT "${CMAKE_OSX_DEPLOYMENT_TARGET}" STREQUAL "" )
+    if(CMAKE_OSX_DEPLOYMENT_TARGET VERSION_LESS 10.15)
+      message(STATUS "EbsdLib: CMAKE_OSX_DEPLOYMENT_TARGET less than 10.15. Enabling EbsdLib_USE_GHC_FILESYSTEM")
+      set(EbsdLib_USE_GHC_FILESYSTEM ON)
+    endif()
   endif()
 endif()
 if("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux" AND ${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 9.0)