CMake: make default install prefix actually work

diff --git a/CMakeLists.txt b/CMakeLists.txt
index f30b0a2ea0df9f88c8720dd753a59f59c56bcd7b..b95fd6280666f98ccadccc6278402bc3da0cffde 100644 (file)
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -4,8 +4,8 @@ list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}/cmake")
 project(NetRadiant C CXX)
 option(BUILD_RADIANT "Build the gui" ON)
 
-if (NOT CMAKE_INSTALL_PREFIX)
-    set(CMAKE_INSTALL_PREFIX "${PROJECT_SOURCE_DIR}/install")
+if (CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
+    set(CMAKE_INSTALL_PREFIX "${PROJECT_SOURCE_DIR}/install" CACHE PATH "..." FORCE)
 endif ()
 
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