diff --git a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
--- a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
@@ -275,8 +275,11 @@
   DenseSet<GlobalValue::GUID> GUIDPreservedSymbols(PreservedSymbols.size());
   for (auto &Entry : PreservedSymbols) {
     StringRef Name = Entry.first();
+    // For MachO object format, symbols are prefixed with "_". For preserved
+    // symbols "_$NAME", we need to preserve the corresponding GUID for "$NAME"
+    // and "\01_$NAME".
     if (TheTriple.isOSBinFormatMachO() && Name.size() > 0 && Name[0] == '_')
-      Name = Name.drop_front();
+      GUIDPreservedSymbols.insert(GlobalValue::getGUID(Name.substr(1)));
     GUIDPreservedSymbols.insert(GlobalValue::getGUID(Name));
   }
   return GUIDPreservedSymbols;
diff --git a/llvm/test/ThinLTO/X86/mangled_symbol.ll b/llvm/test/ThinLTO/X86/mangled_symbol.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/ThinLTO/X86/mangled_symbol.ll
@@ -0,0 +1,20 @@
+; RUN: opt -module-summary %s -o %t1.bc
+; RUN: llvm-lto -thinlto-action=thinlink -o %t.index.bc %t1.bc
+; RUN: llvm-lto -thinlto-action=internalize -thinlto-index %t.index.bc %t1.bc -o - | llvm-dis -o - | FileCheck %s --check-prefix=REGULAR
+; RUN: llvm-lto -thinlto-action=internalize -thinlto-index %t.index.bc %t1.bc -o -  --exported-symbol=_extern_not_mangled --exported-symbol=_extern_mangled | llvm-dis -o - | FileCheck %s --check-prefix=INTERNALIZE
+
+; REGULAR: define void @extern_not_mangled
+; REGULAR: define void @"\01_extern_mangled"
+; INTERNALIZE: define void @extern_not_mangled
+; INTERNALIZE: define void @"\01_extern_mangled"
+
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.11.0"
+
+define void @extern_not_mangled() {
+    ret void
+}
+
+define void @"\01_extern_mangled"() {
+    ret void
+}