Index: lib/Driver/DarwinLdDriver.cpp
===================================================================
--- lib/Driver/DarwinLdDriver.cpp
+++ lib/Driver/DarwinLdDriver.cpp
@@ -738,6 +738,12 @@
     return false;
   }
 
+  // Handle not-yet-supported LTO options
+  if (parsedArgs.getLastArg(OPT_lto_library)) {
+    diagnostics << "warning: -lto_library being ignored. LTO is not yet "
+                   "supported for Mach-O targets\n";
+  }
+
   // Handle -pie or -no_pie
   if (llvm::opt::Arg *pie = parsedArgs.getLastArg(OPT_pie, OPT_no_pie)) {
     switch (ctx.outputMachOType()) {
Index: lib/Driver/DarwinLdOptions.td
===================================================================
--- lib/Driver/DarwinLdOptions.td
+++ lib/Driver/DarwinLdOptions.td
@@ -94,6 +94,9 @@
      HelpText<"Disables the optimisation which merges Objective-C categories "
               "on a class in to the class itself.">,
      Group<grp_opts>;
+def lto_library : Separate<["-"], "lto_library">,
+    MetaVarName<"<path>">,
+    HelpText<"Not yet supported option for LTO">, Group<grp_opts>;
 
 // main executable options
 def grp_main : OptionGroup<"opts">, HelpText<"MAIN EXECUTABLE OPTIONS">;
Index: test/darwin/cmdline-lto_library.objtxt
===================================================================
--- /dev/null
+++ test/darwin/cmdline-lto_library.objtxt
@@ -0,0 +1,11 @@
+# RUN: ld64.lld -arch x86_64 -lto_library %t -print-atoms -r %s 2>&1 | FileCheck %s
+#
+# Test that the -lto_library option results in a warning, not an error.
+#
+
+# CHECK: warning: -lto_library being ignored
+
+--- !native
+defined-atoms:
+    - name:              _foo
+...