diff --git a/CMakeLists.txt b/CMakeLists.txt
index 61f43296..8fa2f3aa 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -13,7 +13,7 @@ include(GNUInstallDirs)
 include(CTest)
 
 if(CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
-  set(CMAKE_INSTALL_PREFIX ${CMAKE_SOURCE_DIR}/InstallArea/ CACHE PATH
+  set(CMAKE_INSTALL_PREFIX ${PROJECT_SOURCE_DIR}/InstallArea/ CACHE PATH
     "Install path prefix, prepended onto install directories." FORCE )
 endif()