diff --git a/CMakeLists.txt b/CMakeLists.txt
index 418dfa8..a62c753 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -140,7 +140,7 @@
       if(NOT EXISTS "${PROJ_DIR}" OR NOT IS_DIRECTORY "${PROJ_DIR}")
         message(FATAL_ERROR "LLVM_ENABLE_PROJECTS requests ${proj} but directory not found: ${PROJ_DIR}")
       endif()
-      set(LLVM_EXTERNAL_${upper_proj}_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../${proj}")
+      set(LLVM_EXTERNAL_${upper_proj}_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../${proj}" CACHE STRING "")
     else()
       message(STATUS "${proj} project is disabled")
       set(SHOULD_ENABLE_PROJECT FALSE)