diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3c055132..53afc513 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,4 +1,5 @@
 cmake_minimum_required(VERSION 3.8...3.28)
+include_guard(GLOBAL)
 
 # Fallback for using newer policies on CMake <3.12.
 if (${CMAKE_VERSION} VERSION_LESS 3.12)