diff --git a/CMakeLists.txt b/CMakeLists.txt
index ea96425..a8ce453 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -52,7 +52,9 @@ endif()
 
 add_library(ut INTERFACE)
 
-set(INCLUDE_INSTALL_DIR include/${PROJECT_NAME}-${PROJECT_VERSION}/include)
+if(NOT DEFINED INCLUDE_INSTALL_DIR)
+  set(INCLUDE_INSTALL_DIR include/${PROJECT_NAME}-${PROJECT_VERSION}/include)
+endif()
 # XXX variant: set(INCLUDE_INSTALL_DIR include)
 target_include_directories(ut INTERFACE $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include> $<INSTALL_INTERFACE:${INCLUDE_INSTALL_DIR}>)
 if(APPLE)