diff --git a/CMakeLists.txt b/CMakeLists.txt
index a1397dc..df35846 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -2,6 +2,9 @@
 
 project(VulkanMemoryAllocator)
 
+# https://cmake.org/cmake/help/latest/variable/PROJECT_IS_TOP_LEVEL.html
+string(COMPARE EQUAL ${CMAKE_CURRENT_SOURCE_DIR} ${CMAKE_SOURCE_DIR} PROJECT_IS_TOP_LEVEL)
+
 if(PROJECT_IS_TOP_LEVEL)
     find_package(Vulkan REQUIRED)
 endif()