diff --git a/clang/docs/ClangCommandLineReference.rst b/clang/docs/ClangCommandLineReference.rst
--- a/clang/docs/ClangCommandLineReference.rst
+++ b/clang/docs/ClangCommandLineReference.rst
@@ -875,7 +875,7 @@
 
 .. option:: -flegacy-pass-manager, -fno-experimental-new-pass-manager, -fno-legacy-pass-manager
 
-Use the legacy pass manager in LLVM
+Use the legacy pass manager in LLVM (deprecated, to be removed in a future release)
 
 .. option:: -fno-crash-diagnostics
 
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -1874,7 +1874,7 @@
   Alias<fglobal_isel>;
 defm legacy_pass_manager : BoolOption<"f", "legacy-pass-manager",
   CodeGenOpts<"LegacyPassManager">, Default<"!static_cast<unsigned>(LLVM_ENABLE_NEW_PASS_MANAGER)">,
-  PosFlag<SetTrue, [], "Use the legacy pass manager in LLVM">,
+  PosFlag<SetTrue, [], "Use the legacy pass manager in LLVM (deprecated, to be removed in a future release)">,
   NegFlag<SetFalse, [], "Use the new pass manager in LLVM">,
   BothFlags<[CC1Option]>>, Group<f_clang_Group>;
 def fexperimental_new_pass_manager : Flag<["-"], "fexperimental-new-pass-manager">,