diff --git a/lib/Driver/ToolChains.cpp b/lib/Driver/ToolChains.cpp
index 4bb3246..80dea50 100644
--- a/lib/Driver/ToolChains.cpp
+++ b/lib/Driver/ToolChains.cpp
@@ -663,6 +663,11 @@
   return 0;
 }
 
+bool Darwin::SupportsObjCGC() const {
+  // Garbage collection is supported everywhere except on iPhone OS.
+  return !isTargetIPhoneOS();
+}
+
 /// Generic_GCC - A tool chain using the 'gcc' command to perform
 /// all subcommands; this relies on gcc translating the majority of
 /// command line options.
diff --git a/lib/Driver/ToolChains.h b/lib/Driver/ToolChains.h
index 0d5b2a3..9e61b89 100644
--- a/lib/Driver/ToolChains.h
+++ b/lib/Driver/ToolChains.h
@@ -176,6 +176,8 @@
   virtual const char *GetDefaultRelocationModel() const;
   virtual const char *GetForcedPicModel() const;
 
+  virtual bool SupportsObjCGC() const;
+
   virtual bool UseDwarfDebugFlags() const;
 
   virtual bool UseSjLjExceptions() const;
diff --git a/lib/Driver/Tools.cpp b/lib/Driver/Tools.cpp
index be79e79..6a74ff4 100644
--- a/lib/Driver/Tools.cpp
+++ b/lib/Driver/Tools.cpp
@@ -1107,10 +1107,23 @@
                     options::OPT_fno_lax_vector_conversions))
     CmdArgs.push_back("-fno-lax-vector-conversions");
 
+  // Handle -fobjc-gc and -fobjc-gc-only. They are exclusive, and -fobjc-gc-only
+  // takes precedence.
+  const Arg *GCArg = Args.getLastArg(options::OPT_fobjc_gc_only);
+  if (!GCArg)
+    GCArg = Args.getLastArg(options::OPT_fobjc_gc);
+  if (GCArg) {
+    if (getToolChain().SupportsObjCGC()) {
+      GCArg->render(Args, CmdArgs);
+    } else {
+      // FIXME: We should move this to a hard error.
+      D.Diag(clang::diag::warn_drv_objc_gc_unsupported)
+        << GCArg->getAsString(Args);
+    }
+  }
+
   Args.AddLastArg(CmdArgs, options::OPT_fno_caret_diagnostics);
   Args.AddLastArg(CmdArgs, options::OPT_fno_show_column);
-  Args.AddLastArg(CmdArgs, options::OPT_fobjc_gc_only);
-  Args.AddLastArg(CmdArgs, options::OPT_fobjc_gc);
   Args.AddLastArg(CmdArgs, options::OPT_fobjc_sender_dependent_dispatch);
   Args.AddLastArg(CmdArgs, options::OPT_fdiagnostics_print_source_range_info);
   Args.AddLastArg(CmdArgs, options::OPT_ftime_report);