diff --git a/CMakeLists.txt b/CMakeLists.txt
index f4b2d4fde8..6e135a5f00 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -334,6 +334,7 @@ foreach(module ${config_module_list})
 	if(external_module)
 		STRING(REGEX REPLACE "//" "/" EXT_MODULE ${module})
 		STRING(REGEX REPLACE "/" "__" EXT_MODULE_PREFIX ${EXT_MODULE})
+		get_filename_component(EXT_MODULE ${module} NAME)
 		add_subdirectory(${module} ${CMAKE_BINARY_DIR}/${EXT_MODULE_PREFIX})
 	else()
 		add_subdirectory(src/${module})