diff --git a/test_package/CMakeLists.txt b/test_package/CMakeLists.txt
index 5b0dc1ae..8a5eec85 100644
--- a/test_package/CMakeLists.txt
+++ b/test_package/CMakeLists.txt
@@ -21,7 +21,9 @@
 # SOFTWARE.
 
 cmake_minimum_required(VERSION 3.15)
-project(test_package)
+project(test_package
+  LANGUAGES CXX
+)
 
 find_package(mp-units CONFIG REQUIRED)