diff --git a/CMakeLists.txt b/CMakeLists.txt
index 69673d5..28b2771 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,5 +1,9 @@
 cmake_minimum_required(VERSION 3.5)
 
+# See https://cmake.org/cmake/help/latest/policy/CMP0077.html
+# This allows for setting option variables externally, when this project
+# is included in another CMake project.
+cmake_policy(SET CMP0077 NEW)
 
 project(inja LANGUAGES CXX VERSION 3.4.0)