Index: lib/LTO/LTOCodeGenerator.cpp
===================================================================
--- lib/LTO/LTOCodeGenerator.cpp
+++ lib/LTO/LTOCodeGenerator.cpp
@@ -64,16 +64,10 @@
 #endif
 }
 
-static void handleLTODiagnostic(const DiagnosticInfo &DI) {
-  DiagnosticPrinterRawOStream DP(errs());                                
-  DI.print(DP);                                                          
-  errs() << "\n";
-}
-
 LTOCodeGenerator::LTOCodeGenerator()
     : Context(getGlobalContext()),
       MergedModule(new Module("ld-temp.o", Context)),
-      IRLinker(MergedModule.get(), handleLTODiagnostic) {
+      IRLinker(MergedModule.get()) {
   initializeLTOPasses();
 }
 
@@ -80,7 +74,7 @@
 LTOCodeGenerator::LTOCodeGenerator(std::unique_ptr<LLVMContext> Context)
     : OwnedContext(std::move(Context)), Context(*OwnedContext),
       MergedModule(new Module("ld-temp.o", *OwnedContext)),
-      IRLinker(MergedModule.get(), handleLTODiagnostic) {
+      IRLinker(MergedModule.get()) {
   initializeLTOPasses();
 }
 
Index: test/LTO/X86/diagnostic-handler-noexit.ll
===================================================================
--- test/LTO/X86/diagnostic-handler-noexit.ll
+++ test/LTO/X86/diagnostic-handler-noexit.ll
@@ -4,10 +4,10 @@
 
 ; RUN: llvm-as <%s >%t1
 ; RUN: llvm-as <%s >%t2
-; RUN: not llvm-lto -o /dev/null %t1 %t2 2>&1 | FileCheck %s
+; RUN: not llvm-lto -use-diagnostic-handler -o /dev/null %t1 %t2 2>&1 | FileCheck %s
 
 target triple = "x86_64-unknown-linux-gnu"
 
-; CHECK: Linking globals named 'goodboy': symbol multiply defined!
+; CHECK: error: Linking globals named 'goodboy': symbol multiply defined!
 ; CHECK: llvm-lto{{.*}}: error adding file
 @goodboy = global i32 3203383023, align 4    ; 0xbeefbeef
Index: tools/lto/lto.cpp
===================================================================
--- tools/lto/lto.cpp
+++ tools/lto/lto.cpp
@@ -85,13 +85,21 @@
 
 namespace {
 
+static void handleLibLTODiagnostic(lto_codegen_diagnostic_severity_t Severity,
+                                   const char *Msg, void *) {
+  sLastErrorString = Msg;
+  sLastErrorString += "\n";
+}
+
 // This derived class owns the native object file. This helps implement the
 // libLTO API semantics, which require that the code generator owns the object
 // file.
 struct LibLTOCodeGenerator : LTOCodeGenerator {
-  LibLTOCodeGenerator() {}
+  LibLTOCodeGenerator() {
+    setDiagnosticHandler(handleLibLTODiagnostic, nullptr); }
   LibLTOCodeGenerator(std::unique_ptr<LLVMContext> Context)
-      : LTOCodeGenerator(std::move(Context)) {}
+      : LTOCodeGenerator(std::move(Context)) {
+    setDiagnosticHandler(handleLibLTODiagnostic, nullptr); }
 
   std::unique_ptr<MemoryBuffer> NativeObjectFile;
 };