Index: docs/Modules.rst
===================================================================
--- docs/Modules.rst
+++ docs/Modules.rst
@@ -466,6 +466,8 @@
 *target feature*
   A specific target feature (e.g., ``sse4``, ``avx``, ``neon``) is available.
 
+*platform variant*
+  A specific os/platform variant (e.g. ``ios``, ``macos``, ``android``, ``win32``, ``linux``, etc) is available.
 
 **Example:** The ``std`` module can be extended to also include C++ and C++11 headers using a *requires-declaration*:
 
Index: lib/Basic/Module.cpp
===================================================================
--- lib/Basic/Module.cpp
+++ lib/Basic/Module.cpp
@@ -93,7 +93,8 @@
                         .Case("opencl", LangOpts.OpenCL)
                         .Case("tls", Target.isTLSSupported())
                         .Case("zvector", LangOpts.ZVector)
-                        .Default(Target.hasFeature(Feature));
+                        .Default(Target.hasFeature(Feature) ||
+                                 Target.getPlatformName() == Feature);
   if (!HasFeature)
     HasFeature = std::find(LangOpts.ModuleFeatures.begin(),
                            LangOpts.ModuleFeatures.end(),
Index: test/Modules/target-platform-features.m
===================================================================
--- /dev/null
+++ test/Modules/target-platform-features.m
@@ -0,0 +1,33 @@
+// Clear and create directories
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: mkdir %t/cache
+// RUN: mkdir %t/Inputs
+
+// Build module map file
+// RUN: echo "module RequiresMacOS {"     >> %t/Inputs/module.map
+// RUN: echo "  requires macos"   >> %t/Inputs/module.map
+// RUN: echo "}"                        >> %t/Inputs/module.map
+// RUN: echo "module RequiresNotiOS {"     >> %t/Inputs/module.map
+// RUN: echo "  requires !ios"   >> %t/Inputs/module.map
+// RUN: echo "}"                        >> %t/Inputs/module.map
+// RUN: echo "module RequiresMain {"     >> %t/Inputs/module.map
+// RUN: echo "  module SubRequiresNotiOS {"     >> %t/Inputs/module.map
+// RUN: echo "    requires !ios"   >> %t/Inputs/module.map
+// RUN: echo "  }"                        >> %t/Inputs/module.map
+// RUN: echo "}"                        >> %t/Inputs/module.map
+
+// RUN: %clang_cc1 -triple=x86_64-apple-macosx10.6 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/cache -x objective-c -I%t/Inputs -verify %s -fblocks -fobjc-arc
+// expected-no-diagnostics
+
+// RUN: not %clang_cc1 -triple=arm64-apple-ios -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/cache -x objective-c -I%t/Inputs %s -fblocks -fobjc-arc 2> %t.notios
+// RUN: FileCheck %s -check-prefix=CHECK-IOS < %t.notios
+
+// CHECK-IOS: module 'RequiresMacOS' requires feature 'macos'
+@import RequiresMacOS;
+// CHECK-IOS: module 'RequiresNotiOS' is incompatible with feature 'ios'
+@import RequiresNotiOS;
+
+// We should never get errors for submodules that don't match
+// CHECK-IOS-NOT: module 'RequiresMain'
+@import RequiresMain;