diff --git a/CMakeLists.txt b/CMakeLists.txt
index eb361e0..5894a42 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -539,7 +539,7 @@ write_basic_package_version_file(
 	VERSION ${PROJECT_VERSION}
 	COMPATIBILITY AnyNewerVersion)
 
-if(BUILD_TESTING)
+if(BUILD_TESTING AND PROJECT_IS_TOP_LEVEL)
 	add_subdirectory(test)
 endif()