diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5cee9176..0907da8c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,5 +1,5 @@
 # Set minimum CMake required version for this project.
-cmake_minimum_required(VERSION 3.13 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.21 FATAL_ERROR)
 
 # Define a C++ project.
 project(RtAudio LANGUAGES CXX)
@@ -306,6 +306,10 @@ endif()
 string(REPLACE ";" " " apilist "${API_LIST}")
 message(STATUS "Compiling with support for: ${apilist}")
 
+if(NOT PROJECT_IS_TOP_LEVEL)
+  return()
+endif()
+
 # PkgConfig file
 string(REPLACE ";" " " req "${PKGCONFIG_REQUIRES}")
 string(REPLACE ";" " " req_libs "${LIBS_REQUIRES}")