diff --git a/llvm/cmake/modules/AddLLVM.cmake b/llvm/cmake/modules/AddLLVM.cmake
--- a/llvm/cmake/modules/AddLLVM.cmake
+++ b/llvm/cmake/modules/AddLLVM.cmake
@@ -1658,8 +1658,9 @@
         set(${file_name} ${LIT_FILE_NAME} PARENT_SCOPE)
         set(${base_dir} ${LIT_BASE_DIR} PARENT_SCOPE)
         return()
-      else()
+      elseif (NOT DEFINED CACHE{LLVM_EXTERNAL_LIT_MISSING_WARNED_ONCE})
         message(WARNING "LLVM_EXTERNAL_LIT set to ${LLVM_EXTERNAL_LIT}, but the path does not exist.")
+        set(LLVM_EXTERNAL_LIT_MISSING_WARNED_ONCE YES CACHE INTERNAL "")
       endif()
     endif()
   endif()