Index: docs/Modules.rst
===================================================================
--- docs/Modules.rst
+++ docs/Modules.rst
@@ -207,6 +207,9 @@
 ``-fmodules-search-all``
   If a symbol is not found, search modules referenced in the current module maps but not imported for symbols, so the error message can reference the module by name.  Note that if the global module index has not been built before, this might take some time as it needs to build all the modules.  Note that this option doesn't apply in module builds, to avoid the recursion.
 
+``-fno-modules-implicit-maps``
+  Suppresses the implicit search for files called ``module.map`` and similar. Instead, module files need to be explicitly specified via ``-fmodule-map-file`` or transitively used.
+
 Module Semantics
 ================
 
Index: include/clang/Basic/LangOptions.def
===================================================================
--- include/clang/Basic/LangOptions.def
+++ include/clang/Basic/LangOptions.def
@@ -126,6 +126,7 @@
 LANGOPT(ModulesSearchAll  , 1, 1, "search even non-imported modules to find unresolved references")
 LANGOPT(ModulesStrictDeclUse, 1, 0, "require declaration of module uses and all headers to be in modules")
 LANGOPT(ModulesErrorRecovery, 1, 1, "automatically import modules as needed when performing error recovery")
+LANGOPT(ModulesImplicitMaps, 1, 1, "use files called module.map implicitly as module maps")
 COMPATIBLE_LANGOPT(Optimize          , 1, 0, "__OPTIMIZE__ predefined macro")
 COMPATIBLE_LANGOPT(OptimizeSize      , 1, 0, "__OPTIMIZE_SIZE__ predefined macro")
 LANGOPT(Static            , 1, 0, "__STATIC__ predefined macro (as opposed to __DYNAMIC__)")
Index: include/clang/Driver/Options.td
===================================================================
--- include/clang/Driver/Options.td
+++ include/clang/Driver/Options.td
@@ -675,6 +675,9 @@
   HelpText<"Like -fmodules-decluse but requires all headers to be in modules">;
 def fno_modules_search_all : Flag <["-"], "fno-modules-search-all">, Group<f_Group>,
   Flags<[DriverOption, CC1Option]>;
+def fno_modules_implicit_maps :
+  Flag <["-"], "fno-modules-implicit-maps">,
+  Group<f_Group>, Flags<[DriverOption, CC1Option]>;
 def fretain_comments_from_system_headers : Flag<["-"], "fretain-comments-from-system-headers">, Group<f_Group>, Flags<[CC1Option]>;
 
 def fmudflapth : Flag<["-"], "fmudflapth">, Group<f_Group>;
Index: include/clang/Lex/HeaderSearch.h
===================================================================
--- include/clang/Lex/HeaderSearch.h
+++ include/clang/Lex/HeaderSearch.h
@@ -252,7 +252,7 @@
   unsigned NumMultiIncludeFileOptzn;
   unsigned NumFrameworkLookups, NumSubFrameworkLookups;
 
-  bool EnabledModules;
+  const LangOptions &LangOpts;
 
   // HeaderSearch doesn't support default or copy construction.
   HeaderSearch(const HeaderSearch&) LLVM_DELETED_FUNCTION;
@@ -479,7 +479,7 @@
   const HeaderMap *CreateHeaderMap(const FileEntry *FE);
 
   /// Returns true if modules are enabled.
-  bool enabledModules() const { return EnabledModules; }
+  bool enabledModules() const { return LangOpts.Modules; }
 
   /// \brief Retrieve the name of the module file that should be used to 
   /// load the given module.
Index: lib/Frontend/CompilerInvocation.cpp
===================================================================
--- lib/Frontend/CompilerInvocation.cpp
+++ lib/Frontend/CompilerInvocation.cpp
@@ -1462,6 +1462,7 @@
     !Args.hasArg(OPT_fno_modules_search_all) &&
     Args.hasArg(OPT_fmodules_search_all);
   Opts.ModulesErrorRecovery = !Args.hasArg(OPT_fno_modules_error_recovery);
+  Opts.ModulesImplicitMaps = !Args.hasArg(OPT_fno_modules_implicit_maps);
   Opts.CharIsSigned = Opts.OpenCL || !Args.hasArg(OPT_fno_signed_char);
   Opts.WChar = Opts.CPlusPlus && !Args.hasArg(OPT_fno_wchar);
   Opts.ShortWChar = Args.hasFlag(OPT_fshort_wchar, OPT_fno_short_wchar, false);
Index: lib/Lex/HeaderSearch.cpp
===================================================================
--- lib/Lex/HeaderSearch.cpp
+++ lib/Lex/HeaderSearch.cpp
@@ -50,7 +50,8 @@
                            const LangOptions &LangOpts,
                            const TargetInfo *Target)
     : HSOpts(HSOpts), Diags(Diags), FileMgr(SourceMgr.getFileManager()),
-      FrameworkMap(64), ModMap(SourceMgr, Diags, LangOpts, Target, *this) {
+      FrameworkMap(64), ModMap(SourceMgr, Diags, LangOpts, Target, *this),
+      LangOpts(LangOpts) {
   AngledDirIdx = 0;
   SystemDirIdx = 0;
   NoCurDirSearch = false;
@@ -60,8 +61,6 @@
   NumIncluded = 0;
   NumMultiIncludeFileOptzn = 0;
   NumFrameworkLookups = NumSubFrameworkLookups = 0;
-
-  EnabledModules = LangOpts.Modules;
 }
 
 HeaderSearch::~HeaderSearch() {
@@ -1172,6 +1171,8 @@
 
 const FileEntry *
 HeaderSearch::lookupModuleMapFile(const DirectoryEntry *Dir, bool IsFramework) {
+  if (!LangOpts.ModulesImplicitMaps)
+    return nullptr;
   // For frameworks, the preferred spelling is Modules/module.modulemap, but
   // module.map at the framework root is also accepted.
   SmallString<128> ModuleMapFileName(Dir->getName());
Index: test/Modules/no-implicit-maps.cpp
===================================================================
--- /dev/null
+++ test/Modules/no-implicit-maps.cpp
@@ -0,0 +1,3 @@
+// RUN: rm -rf %t
+// RUN: %clang_cc1 -x objective-c -fno-modules-implicit-maps -fmodules-cache-path=%t -fmodules -I %S/Inputs/private %s -verify
+@import libPrivate1;  // expected-error {{not found}}