diff --git a/CMakeLists.txt b/CMakeLists.txt
index babb32f119..de40abfd08 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -332,8 +332,9 @@ set(module_libraries)
 foreach(module ${config_module_list})
 	string(REGEX MATCH "^[./]" external_module ${module})
 	if(external_module)
-		get_filename_component(EXT_MODULE ${module} NAME)
-		add_subdirectory(${module} ${CMAKE_BINARY_DIR}/external_mod/${EXT_MODULE})
+		STRING(REGEX REPLACE "//" "/" EXT_MODULE ${module})
+		STRING(REGEX REPLACE "/" "__" EXT_MODULE_PREFIX ${EXT_MODULE})
+		add_subdirectory(${module} ${CMAKE_BINARY_DIR}/${EXT_MODULE_PREFIX})
 	else() 
 		add_subdirectory(src/${module})
 	endif()