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
@@ -5918,12 +5918,14 @@
           "duplicating work in competing clang invocations.">>;
 // FIXME: We only need this in C++ modules / Modules TS if we might textually
 // enter a different module (eg, when building a header unit).
-def fmodules_local_submodule_visibility :
-  Flag<["-"], "fmodules-local-submodule-visibility">,
-  HelpText<"Enforce name visibility rules across submodules of the same "
-           "top-level module.">,
-  MarshallingInfoFlag<LangOpts<"ModulesLocalVisibility">>,
-  ImpliedByAnyOf<[fmodules_ts.KeyPath, fcxx_modules.KeyPath]>;
+defm modules_local_submodule_visibility :
+  BoolFOption<"modules-local-submodule-visibility",
+    LangOpts<"ModulesLocalVisibility">,
+    Default<!strconcat("(", fmodules_ts.KeyPath, "||", fcxx_modules.KeyPath,
+                       ") && !LangOpts->ObjC")>,
+    PosFlag<SetTrue, [], "name visibility rules across submodules of the same "
+                         "top-level module">,
+    NegFlag<SetFalse>>;
 def fmodules_codegen :
   Flag<["-"], "fmodules-codegen">,
   HelpText<"Generate code for uses of this module that assumes an explicit "
diff --git a/clang/test/Modules/cxx20-disable.cpp b/clang/test/Modules/cxx20-disable.cpp
--- a/clang/test/Modules/cxx20-disable.cpp
+++ b/clang/test/Modules/cxx20-disable.cpp
@@ -1,5 +1,5 @@
 // RUN: rm -rf %t && mkdir %t
-// RUN: %clang_cc1 -x objective-c++ -std=c++20                  -I %t %s -verify=enabled
+// RUN: %clang_cc1 -x objective-c++ -std=c++20                  -I %t %s -verify=enabled -fmodules-local-submodule-visibility
 // RUN: %clang_cc1 -x objective-c++ -std=c++20 -fno-cxx-modules -I %t %s -verify=disabled
 
 // enabled-no-diagnostics
diff --git a/clang/test/Modules/fno-modules-local-submodule-visibility.mm b/clang/test/Modules/fno-modules-local-submodule-visibility.mm
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/fno-modules-local-submodule-visibility.mm
@@ -0,0 +1,35 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: %clang_cc1 -std=c++20 -fmodules -fimplicit-module-maps \
+// RUN:   -fmodules-cache-path=%t -fsyntax-only -I %t/include -x objective-c++ \
+// RUN:   %t/tu.m -verify
+// RUN: %clang_cc1 -std=c++20 -fmodules -fimplicit-module-maps \
+// RUN:   -fmodules-cache-path=%t -fsyntax-only -I %t/include -x objective-c++ \
+// RUN:   %t/tu2.m -verify -fmodules-local-submodule-visibility
+
+//--- include/module.modulemap
+
+module M {
+  module A {
+    header "A.h"
+    export *
+  }
+  module B {
+    header "B.h"
+    export *
+  }
+}
+
+//--- include/A.h
+#define A 1
+
+//--- include/B.h
+inline int B = A;
+
+//--- tu.m
+@import M;
+int i = B;
+// expected-no-diagnostics
+
+//--- tu2.m
+@import M; // expected-error {{could not build module 'M'}}
diff --git a/clang/test/Modules/import-syntax.c b/clang/test/Modules/import-syntax.c
--- a/clang/test/Modules/import-syntax.c
+++ b/clang/test/Modules/import-syntax.c
@@ -8,7 +8,7 @@
 // RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fimplicit-module-maps -I%S/Inputs -verify -x objective-c++ -DAT_IMPORT=1 %s
 //
 // RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fimplicit-module-maps -I%S/Inputs -verify -x c++ -fmodules-ts -DIMPORT=1 %s
-// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fimplicit-module-maps -I%S/Inputs -verify -x objective-c++ -fmodules-ts -DIMPORT=1 %s
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fimplicit-module-maps -I%S/Inputs -fmodules-local-submodule-visibility -verify -x objective-c++ -fmodules-ts -DIMPORT=1 %s
 //
 // RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fimplicit-module-maps -I%S/Inputs -verify -x c -DPRAGMA %s
 // RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fimplicit-module-maps -I%S/Inputs -verify -x objective-c -DPRAGMA %s