diff --git a/llvm/test/tools/llvm-ar/lto-kind-from-triple.test b/llvm/test/tools/llvm-ar/lto-kind-from-triple.test
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-ar/lto-kind-from-triple.test
@@ -0,0 +1,20 @@
+## Ensure that we generate a GNU style archive if the first input is a bitcode
+## file with a GNU target triple (absence of __.SYMDEF in the archive).
+
+# RUN: echo -e 'target triple = "x86_64-unknown-linux-gnu" \n define void @_Z3foov() { ret void }' > %t.gnu.ll
+# RUN: llvm-as -o %t.o %t.gnu.ll
+
+# RUN: rm -f %t.ar
+# RUN: llvm-ar crs %t.ar %t.o
+# RUN: not grep -q __.SYMDEF %t.ar
+
+## Ensure that we generate a MachO style archive if the first input is a
+## bitcode file with a MachO target triple (presence of __.SYMDEF in the
+## archive).
+
+# RUN: echo -e 'target triple = "x86_64-apple-macosx10.9" \n define void @_Z3foov() { ret void }' > %t.macho.ll
+# RUN: llvm-as -o %t.o %t.macho.ll
+
+# RUN: rm -f %t.ar
+# RUN: llvm-ar crs %t.ar %t.o
+# RUN: grep -q __.SYMDEF %t.ar
diff --git a/llvm/tools/llvm-ar/llvm-ar.cpp b/llvm/tools/llvm-ar/llvm-ar.cpp
--- a/llvm/tools/llvm-ar/llvm-ar.cpp
+++ b/llvm/tools/llvm-ar/llvm-ar.cpp
@@ -14,11 +14,14 @@
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/ADT/Triple.h"
+#include "llvm/BinaryFormat/Magic.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/Object/Archive.h"
 #include "llvm/Object/ArchiveWriter.h"
+#include "llvm/Object/IRObjectFile.h"
 #include "llvm/Object/MachO.h"
 #include "llvm/Object/ObjectFile.h"
+#include "llvm/Object/SymbolicFile.h"
 #include "llvm/Support/Chrono.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/ConvertUTF.h"
@@ -875,8 +878,9 @@
 }
 
 static object::Archive::Kind getKindFromMember(const NewArchiveMember &Member) {
+  auto MemBufferRef = Member.Buf->getMemBufferRef();
   Expected<std::unique_ptr<object::ObjectFile>> OptionalObject =
-      object::ObjectFile::createObjectFile(Member.Buf->getMemBufferRef());
+      object::ObjectFile::createObjectFile(MemBufferRef);
 
   if (OptionalObject)
     return isa<object::MachOObjectFile>(**OptionalObject)
@@ -885,6 +889,24 @@
 
   // squelch the error in case we had a non-object file
   consumeError(OptionalObject.takeError());
+
+  // If we're adding a bitcode file to the archive, detect the Archive kind
+  // based on the target triple.
+  LLVMContext Context;
+  if (identify_magic(MemBufferRef.getBuffer()) == file_magic::bitcode) {
+    auto ObjOrErr = object::SymbolicFile::createSymbolicFile(
+        MemBufferRef, file_magic::bitcode, &Context);
+    if (ObjOrErr) {
+      auto &IRObject = cast<object::IRObjectFile>(**ObjOrErr);
+      Triple TargetTriple(IRObject.getTargetTriple());
+      return TargetTriple.isOSBinFormatMachO()
+          ? object::Archive::K_DARWIN
+          : object::Archive::K_GNU;
+    }
+    // squelch the error in case this was not a SymbolicFile.
+    consumeError(ObjOrErr.takeError());
+  }
+
   return getDefaultForHost();
 }