diff --git a/lld/MachO/Config.h b/lld/MachO/Config.h
--- a/lld/MachO/Config.h
+++ b/lld/MachO/Config.h
@@ -92,6 +92,7 @@
   llvm::StringRef mapFile;
   llvm::StringRef outputFile;
   llvm::StringRef ltoObjPath;
+  llvm::StringRef thinLTOJobs;
   bool demangle = false;
   llvm::MachO::Target target;
   PlatformInfo platformInfo;
diff --git a/lld/MachO/Driver.cpp b/lld/MachO/Driver.cpp
--- a/lld/MachO/Driver.cpp
+++ b/lld/MachO/Driver.cpp
@@ -869,8 +869,12 @@
       error(arg->getSpelling() + ": expected a positive integer, but got '" +
             arg->getValue() + "'");
     parallel::strategy = hardware_concurrency(threads);
-    // FIXME: use this to configure ThinLTO concurrency too
+    config->thinLTOJobs = v;
   }
+  if (auto *arg = args.getLastArg(OPT_thinlto_jobs_eq))
+    config->thinLTOJobs = arg->getValue();
+  if (!get_threadpool_strategy(config->thinLTOJobs))
+    error("--thinlto-jobs: invalid job count: " + config->thinLTOJobs);
 
   config->entry = symtab->addUndefined(args.getLastArgValue(OPT_e, "_main"),
                                        /*file=*/nullptr,
diff --git a/lld/MachO/LTO.cpp b/lld/MachO/LTO.cpp
--- a/lld/MachO/LTO.cpp
+++ b/lld/MachO/LTO.cpp
@@ -48,8 +48,8 @@
 }
 
 BitcodeCompiler::BitcodeCompiler() {
-  lto::ThinBackend backend =
-      lto::createInProcessThinBackend(heavyweight_hardware_concurrency());
+  lto::ThinBackend backend = lto::createInProcessThinBackend(
+      heavyweight_hardware_concurrency(config->thinLTOJobs));
   ltoObj = std::make_unique<lto::LTO>(createConfig(), backend);
 }
 
diff --git a/lld/MachO/Options.td b/lld/MachO/Options.td
--- a/lld/MachO/Options.td
+++ b/lld/MachO/Options.td
@@ -23,6 +23,9 @@
 def threads_eq : Joined<["--"], "threads=">,
     HelpText<"Number of threads. '1' disables multi-threading. By default all available hardware threads are used">,
     Group<grp_lld>;
+def thinlto_jobs_eq : Joined<["--"], "thinlto-jobs=">,
+    HelpText<"Number of ThinLTO jobs. Default to --threads=">,
+    Group<grp_lld>;
 def reproduce: Separate<["--"], "reproduce">,
     Group<grp_lld>;
 def reproduce_eq: Joined<["--"], "reproduce=">,
diff --git a/lld/test/MachO/Inputs/time_trace_tid_count.py b/lld/test/MachO/Inputs/time_trace_tid_count.py
new file mode 100644
--- /dev/null
+++ b/lld/test/MachO/Inputs/time_trace_tid_count.py
@@ -0,0 +1,12 @@
+import json, sys
+
+"""
+Usage: time_trace_tid_count.py <event name> < input.json
+
+Returns the number of unique thread IDs that contain the given event of
+interest.
+"""
+
+event_name = sys.argv[1]
+events = json.loads(sys.stdin.read())['traceEvents']
+print(len(set(event['tid'] for event in events if event['name'] == event_name)))
diff --git a/lld/test/MachO/thinlto-jobs.ll b/lld/test/MachO/thinlto-jobs.ll
new file mode 100644
--- /dev/null
+++ b/lld/test/MachO/thinlto-jobs.ll
@@ -0,0 +1,53 @@
+; REQUIRES: x86
+; RUN: rm -rf %t; split-file %s %t
+
+; RUN: opt -module-summary %t/f.s -o %t/f.o
+; RUN: opt -module-summary %t/g.s -o %t/g.o
+
+;; First force single-threaded mode
+; RUN: %lld --time-trace --thinlto-jobs=1 -dylib %t/f.o %t/g.o -o %t/out
+; RUN: %python %S/Inputs/time_trace_tid_count.py OptModule < %t/out.time-trace | FileCheck %s --check-prefix=SINGLE
+
+;; Next force multi-threaded mode
+; RUN: %lld --time-trace --thinlto-jobs=2 -dylib %t/f.o %t/g.o -o %t/out
+; RUN: %python %S/Inputs/time_trace_tid_count.py OptModule < %t/out.time-trace | FileCheck %s --check-prefix=MULTI
+
+;; --thinlto-jobs= defaults to --threads=.
+; RUN: %lld --time-trace --threads=2 -dylib %t/f.o %t/g.o -o %t/out
+; RUN: %python %S/Inputs/time_trace_tid_count.py OptModule < %t/out.time-trace | FileCheck %s --check-prefix=MULTI
+
+;; --thinlto-jobs= overrides --threads=.
+; RUN: %lld --time-trace --threads=1 --thinlto-jobs=2 -dylib %t/f.o %t/g.o -o %t/out
+; RUN: %python %S/Inputs/time_trace_tid_count.py OptModule < %t/out.time-trace | FileCheck %s --check-prefix=MULTI
+
+; SINGLE: 1
+; MULTI: 2
+
+;; Test that we parse `--thinlto-jobs=all`. Not checking the exact number of
+;; threads here since we may be running this test on a single-core machine.
+; RUN: %lld --thinlto-jobs=all -dylib %t/f.o %t/g.o -o /dev/null
+
+;; Test with a bad value
+; RUN: not %lld --thinlto-jobs=foo -dylib %t/f.o %t/g.o -o /dev/null 2>&1 | FileCheck %s --check-prefix=BAD-JOBS
+; BAD-JOBS: error: --thinlto-jobs: invalid job count: foo
+
+;--- f.s
+target triple = "x86_64-apple-darwin"
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+
+declare void @g(...)
+
+define void @f() {
+entry:
+  call void (...) @g()
+  ret void
+}
+
+;--- g.s
+target triple = "x86_64-apple-darwin"
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+
+define void @g() {
+entry:
+  ret void
+}