diff --git a/CMLibExternalProject.cmake b/CMLibExternalProject.cmake
index e223d20..4ba9bdc 100644
--- a/CMLibExternalProject.cmake
+++ b/CMLibExternalProject.cmake
@@ -4,6 +4,10 @@ if(CMAKE_BUILD_TYPE)
   list(APPEND CMLIB_EXT_PROJ_DEFAULT_ARGS -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE})
 endif()
 
+if(CMLIB_MAIN_DIR)
+  list(APPEND CMLIB_EXT_PROJ_DEFAULT_ARGS -DCMLIB_MAIN_DIR=${CMLIB_MAIN_DIR})
+endif()
+
 if(CMAKE_C_COMPILER)
   list(APPEND CMLIB_EXT_PROJ_DEFAULT_ARGS -DCMAKE_C_COMPILER=${CMAKE_C_COMPILER})
 endif()