diff --git a/clang/include/clang/Options/Options.td b/clang/include/clang/Options/Options.td
index 786acd6abbd21..40a6d0d8c2137 100644
--- a/clang/include/clang/Options/Options.td
+++ b/clang/include/clang/Options/Options.td
@@ -7236,11 +7236,14 @@ def cpp : Flag<["-"], "cpp">, Group<f_Group>,
   HelpText<"Enable predefined and command line preprocessor macros">;
 def nocpp : Flag<["-"], "nocpp">, Group<f_Group>,
   HelpText<"Disable predefined and command line preprocessor macros">;
-def module_dir : JoinedOrSeparate<["-"], "module-dir">, MetaVarName<"<dir>">,
+def J : JoinedOrSeparate<["-"], "J">,
+  Flags<[RenderJoined]>,
   HelpText<"Put MODULE files in <dir>">,
   DocBrief<[{This option specifies where to put .mod files for compiled modules.
 It is also added to the list of directories to be searched by an USE statement.
 The default is the current directory.}]>;
+def module_dir : Separate<["-"], "module-dir">, MetaVarName<"<dir>">,
+  Alias<J>;
 
 def ffixed_form : Flag<["-"], "ffixed-form">, Group<f_Group>,
   HelpText<"Process source files in fixed form">;
@@ -7376,11 +7379,6 @@ def fdo_concurrent_to_openmp_EQ : Joined<["-"], "fdo-concurrent-to-openmp=">,
       Values<"none, host, device">;
 } // let Visibility = [FC1Option, FlangOption]
 
-def J : JoinedOrSeparate<["-"], "J">,
-  Flags<[RenderJoined]>, Visibility<[FlangOption, FC1Option]>,
-  Group<gfortran_Group>,
-  Alias<module_dir>;
-
 //===----------------------------------------------------------------------===//
 // FC1 Options
 //===----------------------------------------------------------------------===//
diff --git a/clang/lib/Driver/ToolChains/Flang.cpp b/clang/lib/Driver/ToolChains/Flang.cpp
index 270904de544d6..b49cf0f3ce2bb 100644
--- a/clang/lib/Driver/ToolChains/Flang.cpp
+++ b/clang/lib/Driver/ToolChains/Flang.cpp
@@ -126,7 +126,7 @@ void Flang::addDebugOptions(const llvm::opt::ArgList &Args, const JobAction &JA,
   const auto &TC = getToolChain();
   const Driver &D = TC.getDriver();
   Args.addAllArgs(CmdArgs,
-                  {options::OPT_module_dir, options::OPT_fdebug_module_writer,
+                  {options::OPT_J, options::OPT_fdebug_module_writer,
                    options::OPT_fintrinsic_modules_path, options::OPT_pedantic,
                    options::OPT_std_EQ, options::OPT_W_Joined,
                    options::OPT_fconvert_EQ, options::OPT_fpass_plugin_EQ,
diff --git a/flang/lib/Frontend/CompilerInvocation.cpp b/flang/lib/Frontend/CompilerInvocation.cpp
index 893121fe01f27..94cf50747ac65 100644
--- a/flang/lib/Frontend/CompilerInvocation.cpp
+++ b/flang/lib/Frontend/CompilerInvocation.cpp
@@ -959,7 +959,7 @@ static bool parseSemaArgs(CompilerInvocation &res, llvm::opt::ArgList &args,
 
   // -J/module-dir option
   std::vector<std::string> moduleDirList =
-      args.getAllArgValues(clang::options::OPT_module_dir);
+      args.getAllArgValues(clang::options::OPT_J);
   // User can only specify one -J/-module-dir directory, but may repeat
   // -J/-module-dir as long as the directory is the same each time.
   // https://gcc.gnu.org/onlinedocs/gfortran/Directory-Options.html
diff --git a/flang/test/Driver/write-module.f90 b/flang/test/Driver/write-module.f90
index c4dbaddd4b270..ddced1342f025 100644
--- a/flang/test/Driver/write-module.f90
+++ b/flang/test/Driver/write-module.f90
@@ -3,6 +3,19 @@
 !   * is saved in the _directory specified by the user_
 ! We use `-fsyntax-only` as it stops after the semantic checks (the module file is generated when sema checks are run)
 
+! ------------------------------------------------------------------------------
+! At one time, flang accepted -module-dir<value> (note the lack of a separator
+! between -module-dir and <value>). This is no longer allowed.
+! -module-dir=<value> is also not allowed
+!
+! RUN: not %flang -fsyntax-only -module-dir%t %s 2>&1 \
+! RUN:      | FileCheck %s -check-prefix=JOINED
+!
+! RUN: not %flang -fsyntax-only -module-dir=%t %s 2>&1 \
+! RUN:      | FileCheck %s -check-prefix=JOINED
+!
+! JOINED: error: unknown argument: '-module-dir{{.+}}'
+!
 !--------------------------
 ! -module-dir <value>
 !--------------------------
@@ -10,15 +23,7 @@
 ! RUN: cd %t && %flang -fsyntax-only -module-dir %t/dir-flang %s
 ! RUN: ls %t/dir-flang/testmodule.mod && not ls %t/testmodule.mod
 ! RUN: cd -
-
-!--------------------------
-! -module-dir<value>
-!--------------------------
-! RUN: rm -rf %t && mkdir -p %t/dir-flang
-! RUN: cd %t && %flang -fsyntax-only -module-dir%t/dir-flang %s
-! RUN: ls %t/dir-flang/testmodule.mod && not ls %t/testmodule.mod
-! RUN: cd -
-
+!
 !---------------------------
 ! -J <value>
 !---------------------------