diff --git a/clang/include/clang/Driver/CC1Options.td b/clang/include/clang/Driver/CC1Options.td
index f9a2558..25097e5 100644
--- a/clang/include/clang/Driver/CC1Options.td
+++ b/clang/include/clang/Driver/CC1Options.td
@@ -289,8 +289,8 @@
   HelpText<"Use with -ast-dump or -ast-print to dump/print only AST declaration"
            " nodes having a certain substring in a qualified name. Use"
            " -ast-list to list all filterable declaration node names.">;
-def fmodules_global_index : Flag<["-"], "fmodules-global-index">,
-  HelpText<"Automatically generate or update the global module index">;
+def fno_modules_global_index : Flag<["-"], "fno-modules-global-index">,
+  HelpText<"Do not automatically generate or update the global module index">;
 
 let Group = Action_Group in {
 
diff --git a/clang/include/clang/Frontend/FrontendOptions.h b/clang/include/clang/Frontend/FrontendOptions.h
index 3816211..c39c190 100644
--- a/clang/include/clang/Frontend/FrontendOptions.h
+++ b/clang/include/clang/Frontend/FrontendOptions.h
@@ -213,8 +213,8 @@
     ShowStats(false), ShowTimers(false), ShowVersion(false),
     FixWhatYouCan(false), FixOnlyWarnings(false), FixAndRecompile(false),
     FixToTemporaries(false), ARCMTMigrateEmitARCErrors(false),
-    SkipFunctionBodies(false), UseGlobalModuleIndex(false),
-    GenerateGlobalModuleIndex(false),
+    SkipFunctionBodies(false), UseGlobalModuleIndex(true),
+    GenerateGlobalModuleIndex(true),
     ARCMTAction(ARCMT_None), ObjCMTAction(ObjCMT_None),
     ProgramAction(frontend::ParseSyntaxOnly)
   {}
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 9c965c0..b200637 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -689,7 +689,7 @@
   Opts.FixAndRecompile = Args.hasArg(OPT_fixit_recompile);
   Opts.FixToTemporaries = Args.hasArg(OPT_fixit_to_temp);
   Opts.ASTDumpFilter = Args.getLastArgValue(OPT_ast_dump_filter);
-  Opts.UseGlobalModuleIndex = Args.hasArg(OPT_fmodules_global_index);
+  Opts.UseGlobalModuleIndex = !Args.hasArg(OPT_fno_modules_global_index);
   Opts.GenerateGlobalModuleIndex = Opts.UseGlobalModuleIndex;
   
   Opts.CodeCompleteOpts.IncludeMacros
diff --git a/clang/test/Modules/global_index.m b/clang/test/Modules/global_index.m
index 53bee03..51a007f 100644
--- a/clang/test/Modules/global_index.m
+++ b/clang/test/Modules/global_index.m
@@ -1,12 +1,12 @@
 // RUN: rm -rf %t
 // Run without global module index
-// RUN: %clang_cc1 -Wauto-import -fmodule-cache-path %t -fdisable-module-hash -fmodules -F %S/Inputs %s -verify
+// RUN: %clang_cc1 -Wauto-import -fmodule-cache-path %t -fdisable-module-hash -fmodules -fno-modules-global-index -F %S/Inputs %s -verify
 // RUN: ls %t|not grep modules.idx
 // Run and create the global module index
-// RUN: %clang_cc1 -Wauto-import -fmodule-cache-path %t -fdisable-module-hash -fmodules -fmodules-global-index -F %S/Inputs %s -verify
+// RUN: %clang_cc1 -Wauto-import -fmodule-cache-path %t -fdisable-module-hash -fmodules -F %S/Inputs %s -verify
 // RUN: ls %t|grep modules.idx
 // Run and use the global module index
-// RUN: %clang_cc1 -Wauto-import -fmodule-cache-path %t -fdisable-module-hash -fmodules -fmodules-global-index -F %S/Inputs %s -verify -print-stats 2>&1 | FileCheck %s
+// RUN: %clang_cc1 -Wauto-import -fmodule-cache-path %t -fdisable-module-hash -fmodules -F %S/Inputs %s -verify -print-stats 2>&1 | FileCheck %s
 
 // expected-no-diagnostics
 @import DependsOnModule;