Index: lld/COFF/Driver.h
===================================================================
--- lld/COFF/Driver.h
+++ lld/COFF/Driver.h
@@ -79,6 +79,7 @@
 
 private:
   std::unique_ptr<llvm::TarWriter> Tar; // for /linkrepro
+  std::function<void(StringRef, StringRef)> TakeBufferHook;
 
   // Opens a file. Path has to be resolved already.
   MemoryBufferRef openFile(StringRef Path);
Index: lld/COFF/Driver.cpp
===================================================================
--- lld/COFF/Driver.cpp
+++ lld/COFF/Driver.cpp
@@ -24,6 +24,7 @@
 #include "lld/Common/Timer.h"
 #include "lld/Common/Version.h"
 #include "llvm/ADT/Optional.h"
+#include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/BinaryFormat/Magic.h"
 #include "llvm/Object/ArchiveWriter.h"
@@ -40,6 +41,7 @@
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/ToolDrivers/llvm-lib/LibDriver.h"
 #include <algorithm>
+#include <atomic>
 #include <future>
 #include <memory>
 
@@ -48,6 +50,36 @@
 using namespace llvm::COFF;
 using llvm::sys::Process;
 
+namespace {
+class ReproWriter {
+public:
+  ReproWriter(StringRef OutputFileName, StringRef Prefix)
+      : OutputFileName(OutputFileName), Prefix(Prefix), NeedsWrite(true) {}
+  ~ReproWriter() {
+    if (!std::atomic_exchange(&NeedsWrite, false) || lld::errorCount() == 0)
+      return;
+    Expected<std::unique_ptr<TarWriter>> Tar =
+        TarWriter::create(OutputFileName, Prefix);
+    if (!Tar) {
+      lld::warn("Could not write reproducer to " + OutputFileName + ": " +
+                toString(Tar.takeError()));
+      return;
+    }
+    for (const auto &I : Files)
+      (*Tar)->append(I.getKey(), I.getValue());
+  }
+  void addBuffer(StringRef Path, StringRef Data) {
+    Files.try_emplace(Path, Data);
+  }
+
+private:
+  std::string OutputFileName;
+  StringRef Prefix;
+  StringMap<StringRef> Files;
+  std::atomic_bool NeedsWrite;
+};
+} // anonymous namespace
+
 namespace lld {
 namespace coff {
 
@@ -119,9 +151,10 @@
   MemoryBufferRef MBRef = *MB;
   make<std::unique_ptr<MemoryBuffer>>(std::move(MB)); // take ownership
 
-  if (Driver->Tar)
-    Driver->Tar->append(relativeToRoot(MBRef.getBufferIdentifier()),
-                        MBRef.getBuffer());
+  if (Driver->TakeBufferHook)
+    Driver->TakeBufferHook(relativeToRoot(MBRef.getBufferIdentifier()),
+                           MBRef.getBuffer());
+
   return MBRef;
 }
 
@@ -441,6 +474,7 @@
 
   for (auto *Arg : Args) {
     switch (Arg->getOption().getID()) {
+    case OPT_errorrepro:
     case OPT_linkrepro:
     case OPT_INPUT:
     case OPT_defaultlib:
@@ -740,6 +774,7 @@
 
   for (auto *Arg : Args) {
     switch (Arg->getOption().getID()) {
+    case OPT_errorrepro:
     case OPT_linkrepro:
     case OPT_lldmap:
     case OPT_lldmap_file:
@@ -898,6 +933,23 @@
       error("/linkrepro: failed to open " + Path + ": " +
             toString(ErrOrWriter.takeError()));
     }
+
+    TakeBufferHook = [this](StringRef Path, StringRef Data) {
+      Tar->append(Path, Data);
+    };
+  }
+
+  std::unique_ptr<ReproWriter> ReproWriter;
+  addLldExitHandler([&ReproWriter]() { ReproWriter.reset(); });
+  if (auto *Arg = Args.getLastArg(OPT_errorrepro)) {
+    if (Args.getLastArg(OPT_linkrepro))
+      fatal("/errorrepro must not be specified with /linkrepro");
+    SmallString<64> Path = StringRef(Arg->getValue());
+    sys::path::append(Path, "repro.tar");
+    ReproWriter = make_unique<class ReproWriter>(Path, "repro");
+    TakeBufferHook = [&ReproWriter](StringRef Path, StringRef Data) {
+      ReproWriter->addBuffer(Path, Data);
+    };
   }
 
   if (!Args.hasArg(OPT_INPUT)) {
@@ -1272,10 +1324,11 @@
   if (!Resources.empty())
     Symtab->addFile(make<ObjFile>(convertResToCOFF(Resources)));
 
-  if (Tar)
-    Tar->append("response.txt",
-                createResponseFile(Args, FilePaths,
-                                   ArrayRef<StringRef>(SearchPaths).slice(1)));
+  if (TakeBufferHook)
+    TakeBufferHook(
+        "response.txt",
+        createResponseFile(Args, FilePaths,
+                           ArrayRef<StringRef>(SearchPaths).slice(1)));
 
   // Handle /largeaddressaware
   Config->LargeAddressAware = Args.hasFlag(
Index: lld/COFF/Options.td
===================================================================
--- lld/COFF/Options.td
+++ lld/COFF/Options.td
@@ -139,6 +139,7 @@
 // LLD extensions
 def debug_ghash : F<"debug:ghash">;
 def debug_dwarf : F<"debug:dwarf">;
+def errorrepro : P<"errorrepro", "If linking fails, write repro.tar here">;
 def export_all_symbols : F<"export-all-symbols">;
 def kill_at : F<"kill-at">;
 def lldmingw : F<"lldmingw">;
Index: lld/test/COFF/errorrepro.test
===================================================================
--- /dev/null
+++ lld/test/COFF/errorrepro.test
@@ -0,0 +1,40 @@
+# REQUIRES: x86, shell
+
+# RUN: rm -rf %t.dir
+# RUN: yaml2obj < %p/Inputs/hello32.yaml > %t.obj
+
+# RUN: mkdir -p %t.dir/noerrorrepro
+# RUN: cd %t.dir/noerrorrepro
+# RUN: not lld-link %t.obj -entry:main -out:%t.exe
+# RUN: not test -f repro.tar || (echo 'repro.tar should not exist' >&2; false)
+
+# RUN: mkdir -p %t.dir/noerror
+# RUN: cd %t.dir/noerror
+# RUN: lld-link %t.obj %p/Inputs/std32.lib -errorrepro:. -entry:main -out:%t.exe
+# RUN: not test -f repro.tar || (echo 'repro.tar should not exist' >&2; false)
+
+# RUN: mkdir -p %t.dir/errorrepro
+# RUN: cd %t.dir/errorrepro
+# RUN: not lld-link %t.obj -errorrepro:. -entry:main -out:%t.exe
+# RUN: tar xf repro.tar
+# RUN: diff %t.obj repro/%:t.obj
+# RUN: FileCheck %s --check-prefix=RSP < repro/response.txt
+
+# RUN: mkdir -p %t.dir/fatal
+# RUN: cd %t.dir/fatal
+# RUN: not env LLD_IN_TEST=0 \
+# RUN:     lld-link %t.obj -errorrepro:. -errorlimit:1 -entry:main -out:%t.exe
+# RUN: tar xf repro.tar
+# RUN: diff %t.obj repro/%:t.obj
+# RUN: FileCheck %s --check-prefix=FATALRSP < repro/response.txt
+
+# RSP-NOT: -errorrepro
+# RSP: -entry:main
+# RSP: -out:
+# RSP: errorrepro.test.tmp.obj
+
+# FATALRSP-NOT: -errorrepro
+# FATALRSP: -errorlimit:1
+# FATALRSP: -entry:main
+# FATALRSP: -out:
+# FATALRSP: errorrepro.test.tmp.obj