diff --git a/include/clang/Basic/LangOptions.h b/include/clang/Basic/LangOptions.h
index 84836eb4e5c3ec3e600c521a5c003287ddea33d2..3c9d23efe63b676f7c88525313a56e69f7984a7e 100644
--- a/include/clang/Basic/LangOptions.h
+++ b/include/clang/Basic/LangOptions.h
@@ -102,6 +102,8 @@ public:
 
   /// \brief The names of any features to enable in module 'requires' decls
   /// in addition to the hard-coded list in Module.cpp and the target features.
+  ///
+  /// This list is sorted.
   std::vector<std::string> ModuleFeatures;
 
   /// \brief Options for parsing comments.
diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index 250c992cbde3576885a5e52daa15b5a49c84bedd..dd664ca652f0a203588adda7e8a5b66f96087fda 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -1588,6 +1588,7 @@ static void ParseLangArgs(LangOptions &Opts, ArgList &Args, InputKind IK,
   Opts.ImplementationOfModule =
       Args.getLastArgValue(OPT_fmodule_implementation_of);
   Opts.ModuleFeatures = Args.getAllArgValues(OPT_fmodule_feature);
+  std::sort(Opts.ModuleFeatures.begin(), Opts.ModuleFeatures.end());
   Opts.NativeHalfType |= Args.hasArg(OPT_fnative_half_type);
   Opts.HalfArgsAndReturns = Args.hasArg(OPT_fallow_half_arguments_and_returns);
   Opts.GNUAsm = !Args.hasArg(OPT_fno_gnu_inline_asm);
@@ -1967,6 +1968,9 @@ std::string CompilerInvocation::getModuleHash() const {
 #define BENIGN_LANGOPT(Name, Bits, Default, Description)
 #define BENIGN_ENUM_LANGOPT(Name, Type, Bits, Default, Description)
 #include "clang/Basic/LangOptions.def"
+
+  for (StringRef Feature : LangOpts->ModuleFeatures)
+    code = hash_combine(code, Feature);
   
   // Extend the signature with the target options.
   code = hash_combine(code, TargetOpts->Triple, TargetOpts->CPU,
diff --git a/lib/Frontend/FrontendActions.cpp b/lib/Frontend/FrontendActions.cpp
index 6f202a15483a5a562f116e10ea9b061690bbe616..499776468818449e9bc73727d45f6a94d46cddc5 100644
--- a/lib/Frontend/FrontendActions.cpp
+++ b/lib/Frontend/FrontendActions.cpp
@@ -470,6 +470,13 @@ namespace {
 #define BENIGN_LANGOPT(Name, Bits, Default, Description)
 #define BENIGN_ENUM_LANGOPT(Name, Type, Bits, Default, Description)
 #include "clang/Basic/LangOptions.def"
+
+      if (!LangOpts.ModuleFeatures.empty()) {
+        Out.indent(4) << "Module features:\n";
+        for (StringRef Feature : LangOpts.ModuleFeatures)
+          Out.indent(6) << Feature << "\n";
+      }
+
       return false;
     }
 
diff --git a/lib/Serialization/ASTReader.cpp b/lib/Serialization/ASTReader.cpp
index 7242793be22025966ed35ec24860ce03fa0b24e0..6bdca057badcfc1993a09854536f705777f688bd 100644
--- a/lib/Serialization/ASTReader.cpp
+++ b/lib/Serialization/ASTReader.cpp
@@ -209,6 +209,12 @@ static bool checkLanguageOptions(const LangOptions &LangOpts,
 #define BENIGN_ENUM_LANGOPT(Name, Type, Bits, Default, Description)
 #include "clang/Basic/LangOptions.def"
 
+  if (ExistingLangOpts.ModuleFeatures != LangOpts.ModuleFeatures) {
+    if (Diags)
+      Diags->Report(diag::err_pch_langopt_value_mismatch) << "module features";
+    return true;
+  }
+
   if (ExistingLangOpts.ObjCRuntime != LangOpts.ObjCRuntime) {
     if (Diags)
       Diags->Report(diag::err_pch_langopt_value_mismatch)
@@ -4437,6 +4443,9 @@ bool ASTReader::ParseLanguageOptions(const RecordData &Record,
   LangOpts.Sanitize.set(SanitizerKind::ID, Record[Idx++]);
 #include "clang/Basic/Sanitizers.def"
 
+  for (unsigned N = Record[Idx++]; N; --N)
+    LangOpts.ModuleFeatures.push_back(ReadString(Record, Idx));
+
   ObjCRuntime::Kind runtimeKind = (ObjCRuntime::Kind) Record[Idx++];
   VersionTuple runtimeVersion = ReadVersionTuple(Record, Idx);
   LangOpts.ObjCRuntime = ObjCRuntime(runtimeKind, runtimeVersion);
diff --git a/lib/Serialization/ASTWriter.cpp b/lib/Serialization/ASTWriter.cpp
index 5bb0bec4f5690b1200fb92588ac133812aa6818e..d6267767cf46f5711a8a47266784561c16347098 100644
--- a/lib/Serialization/ASTWriter.cpp
+++ b/lib/Serialization/ASTWriter.cpp
@@ -1266,6 +1266,10 @@ void ASTWriter::WriteControlBlock(Preprocessor &PP, ASTContext &Context,
   Record.push_back(LangOpts.Sanitize.has(SanitizerKind::ID));
 #include "clang/Basic/Sanitizers.def"
 
+  Record.push_back(LangOpts.ModuleFeatures.size());
+  for (StringRef Feature : LangOpts.ModuleFeatures)
+    AddString(Feature, Record);
+
   Record.push_back((unsigned) LangOpts.ObjCRuntime.getKind());
   AddVersionTuple(LangOpts.ObjCRuntime.getVersion(), Record);
   
diff --git a/test/Modules/module-feature.m b/test/Modules/module-feature.m
new file mode 100644
index 0000000000000000000000000000000000000000..4926d26515f860d270d033e99f931d3ff6343e4e
--- /dev/null
+++ b/test/Modules/module-feature.m
@@ -0,0 +1,14 @@
+// RUN: rm -rf %t %t.nohash
+
+// Each set of features gets its own cache.
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fimplicit-module-maps -fmodule-feature f1 -fmodule-feature f2 -F %S/Inputs %s -verify -Rmodule-build
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fimplicit-module-maps -fmodule-feature f2 -F %S/Inputs %s -verify -Rmodule-build
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fimplicit-module-maps -fmodule-feature f2 -fmodule-feature f1 -F %S/Inputs %s -Rmodule-build 2>&1 | FileCheck %s -allow-empty -check-prefix=ALREADY_BUILT
+// ALREADY_BUILT-NOT: building module
+
+// Errors if we try to force the load.
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t.nohash -fimplicit-module-maps -fdisable-module-hash -fmodule-feature f1 -fmodule-feature f2 -F %S/Inputs %s -verify -Rmodule-build
+// RUN: not %clang_cc1 -fmodules -fmodules-cache-path=%t.nohash -fimplicit-module-maps -fdisable-module-hash -fmodule-feature f2 -F %S/Inputs %s 2>&1 | FileCheck %s -check-prefix=DIFFERS
+// DIFFERS: error: module features differs
+
+@import Module; // expected-remark {{building module 'Module'}} expected-remark {{finished}}
diff --git a/test/Modules/module_file_info.m b/test/Modules/module_file_info.m
index 01d5073650b401666bcab4011b77db0ce21843c6..8693d2b89497c2148d57f24156fcc98177c24934 100644
--- a/test/Modules/module_file_info.m
+++ b/test/Modules/module_file_info.m
@@ -2,7 +2,7 @@
 @import DependsOnModule;
 
 // RUN: rm -rf %t
-// RUN: %clang_cc1 -w -Wunused -fmodules -fimplicit-module-maps -fdisable-module-hash -fmodules-cache-path=%t -F %S/Inputs -DBLARG -DWIBBLE=WOBBLE %s
+// RUN: %clang_cc1 -w -Wunused -fmodules -fimplicit-module-maps -fdisable-module-hash -fmodules-cache-path=%t -F %S/Inputs -DBLARG -DWIBBLE=WOBBLE -fmodule-feature myfeature %s
 // RUN: %clang_cc1 -module-file-info %t/DependsOnModule.pcm | FileCheck %s
 
 // CHECK: Generated by this Clang:
@@ -14,6 +14,8 @@
 // CHECK:   C99: Yes
 // CHECK:   Objective-C 1: Yes
 // CHECK:   modules extension to C: Yes
+// CHECK:   Module features:
+// CHECK:     myfeature
 
 // CHECK: Target options:
 // CHECK:     Triple: