Index: lld/MachO/LTO.cpp
===================================================================
--- lld/MachO/LTO.cpp
+++ lld/MachO/LTO.cpp
@@ -138,8 +138,21 @@
       saveBuffer(buf[i], config->outputFile + Twine(i) + ".lto.o");
   }
 
-  if (!config->ltoObjPath.empty())
-    fs::create_directories(config->ltoObjPath);
+  // In ThinLTO mode, Clang passes a temporary directory in -object_path_lto,
+  // while the argument is a single file in FullLTO mode.
+  bool objPathIsDir = true;
+  if (!config->ltoObjPath.empty()) {
+    if (!fs::exists(config->ltoObjPath)) {
+      fs::create_directories(config->ltoObjPath);
+    } else if (!fs::is_directory(config->ltoObjPath)) {
+      objPathIsDir = false;
+
+      unsigned objCount =
+          count_if(buf, [](const SmallString<0> &b) { return !b.empty(); });
+      if (objCount > 1)
+        fatal("-object_path_lto must specify a directory when using ThinLTO");
+    }
+  }
 
   std::vector<ObjFile *> ret;
   for (unsigned i = 0; i != maxTasks; ++i) {
@@ -149,9 +162,10 @@
     uint32_t modTime = 0;
     if (!config->ltoObjPath.empty()) {
       filePath = config->ltoObjPath;
-      path::append(filePath, Twine(i) + "." +
-                                 getArchitectureName(config->arch()) +
-                                 ".lto.o");
+      if (objPathIsDir)
+        path::append(filePath, Twine(i) + "." +
+                                   getArchitectureName(config->arch()) +
+                                   ".lto.o");
       saveBuffer(buf[i], filePath);
       modTime = getModTime(filePath);
     }
Index: lld/test/MachO/lto-object-path.ll
===================================================================
--- lld/test/MachO/lto-object-path.ll
+++ lld/test/MachO/lto-object-path.ll
@@ -8,16 +8,21 @@
 ; RUN: llvm-nm -pa %t/test | FileCheck %s --check-prefixes CHECK,NOOBJPATH
 
 ; RUN: %lld %t/test.o -o %t/test -object_path_lto %t/lto-temps
-; RUN: llvm-nm -pa %t/test | FileCheck %s --check-prefixes CHECK,OBJPATH -DDIR=%t/lto-temps
+; RUN: llvm-nm -pa %t/test | FileCheck %s --check-prefixes CHECK,OBJPATH-DIR -DDIR=%t/lto-temps
 
-; CHECK:          0000000000000000                - 00 0000    SO /tmp/test.cpp
-; NOOBJPATH-NEXT: 0000000000000000                - 03 0001   OSO /tmp/lto.tmp
+; RUN: %lld %t/test.o -o %t/test -object_path_lto %t/lto-tmp.o
+; RUN: llvm-nm -pa %t/test | FileCheck %s --check-prefixes CHECK,OBJPATH-FILE -DFILE=%t/lto-tmp.o
+
+
+; CHECK:             0000000000000000                - 00 0000    SO /tmp/test.cpp
+; NOOBJPATH-NEXT:    0000000000000000                - 03 0001   OSO /tmp/lto.tmp
 ;; check that modTime is nonzero when `-object_path_lto` is provided
-; OBJPATH-NEXT:   {{[0-9a-f]*[1-9a-f]+[0-9a-f]*}} - 03 0001   OSO [[DIR]]/0.x86_64.lto.o
-; CHECK-NEXT:     {{[0-9a-f]+}}                   - 01 0000   FUN _main
-; CHECK-NEXT:     0000000000000001                - 00 0000   FUN
-; CHECK-NEXT:     0000000000000000                - 01 0000    SO
-; CHECK-NEXT:     {{[0-9a-f]+}}                   T _main
+; OBJPATH-DIR-NEXT:  {{[0-9a-f]*[1-9a-f]+[0-9a-f]*}} - 03 0001   OSO [[DIR]]/0.x86_64.lto.o
+; OBJPATH-FILE-NEXT: {{[0-9a-f]*[1-9a-f]+[0-9a-f]*}} - 03 0001   OSO [[FILE]]
+; CHECK-NEXT:        {{[0-9a-f]+}}                   - 01 0000   FUN _main
+; CHECK-NEXT:        0000000000000001                - 00 0000   FUN
+; CHECK-NEXT:        0000000000000000                - 01 0000    SO
+; CHECK-NEXT:        {{[0-9a-f]+}}                   T _main
 
 target triple = "x86_64-apple-macosx10.15.0"
 target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"