diff --git a/clang/test/CMakeLists.txt b/clang/test/CMakeLists.txt
--- a/clang/test/CMakeLists.txt
+++ b/clang/test/CMakeLists.txt
@@ -33,6 +33,7 @@
   "LLVM_LIBS_DIR"
   "SHLIBDIR"
   "LLVM_LIT_TOOLS_DIR"
+  "LLVM_EXTERNAL_LIT"
   "CLANG_BINARY_DIR"
   "CLANG_SOURCE_DIR"
   "CLANG_TOOLS_DIR"
diff --git a/clang/test/lit.site.cfg.py.in b/clang/test/lit.site.cfg.py.in
--- a/clang/test/lit.site.cfg.py.in
+++ b/clang/test/lit.site.cfg.py.in
@@ -34,6 +34,7 @@
 config.use_z3_solver = lit_config.params.get('USE_Z3_SOLVER', "@USE_Z3_SOLVER@")
 config.has_plugins = @LLVM_ENABLE_PLUGINS@
 config.clang_vendor_uti = "@CLANG_VENDOR_UTI@"
+config.llvm_external_lit = path(r"@LLVM_EXTERNAL_LIT@")
 
 # Support substitution of the tools and libs dirs with user parameters. This is
 # used when we can't determine the tool dir at configuration time.
diff --git a/clang/test/utils/update_cc_test_checks/lit.local.cfg b/clang/test/utils/update_cc_test_checks/lit.local.cfg
--- a/clang/test/utils/update_cc_test_checks/lit.local.cfg
+++ b/clang/test/utils/update_cc_test_checks/lit.local.cfg
@@ -19,7 +19,7 @@
 script_path = os.path.join(config.llvm_src_root, 'utils',
                            'update_cc_test_checks.py')
 assert os.path.isfile(script_path)
-lit = shell_quote(os.path.join(config.llvm_src_root, 'utils', 'lit', 'lit.py'))
+lit = config.llvm_external_lit if config.llvm_external_lit else shell_quote(os.path.join(config.llvm_src_root, 'utils', 'lit', 'lit.py'))
 python = shell_quote(config.python_executable)
 config.substitutions.append(
     ('%update_cc_test_checks', "%s %s %s" % (