diff --git a/include/llvm/IR/DIBuilder.h b/include/llvm/IR/DIBuilder.h
index aa43c02d5cd..0137a096e97 100644
--- a/include/llvm/IR/DIBuilder.h
+++ b/include/llvm/IR/DIBuilder.h
@@ -384,6 +384,13 @@ namespace llvm {
                                            DITypeRefArray ParameterTypes,
                                            unsigned Flags = 0);
 
+    /// Create an external type reference.
+    /// \param Tag              Dwarf TAG.
+    /// \param File             File in which the type is defined.
+    /// \param UniqueIdentifier A unique identifier for the type.
+    DICompositeType *createExternalTypeRef(unsigned Tag, DIFile *File,
+                                           StringRef UniqueIdentifier);
+
     /// Create a new DIType* with "artificial" flag set.
     DIType *createArtificialType(DIType *Ty);
 
diff --git a/include/llvm/IR/DebugInfoFlags.def b/include/llvm/IR/DebugInfoFlags.def
index d5de8683fd3..9756c12264b 100644
--- a/include/llvm/IR/DebugInfoFlags.def
+++ b/include/llvm/IR/DebugInfoFlags.def
@@ -32,5 +32,6 @@ HANDLE_DI_FLAG((1 << 11), Vector)
 HANDLE_DI_FLAG((1 << 12), StaticMember)
 HANDLE_DI_FLAG((1 << 13), LValueReference)
 HANDLE_DI_FLAG((1 << 14), RValueReference)
+HANDLE_DI_FLAG((1 << 15), ExternalTypeRef)
 
 #undef HANDLE_DI_FLAG
diff --git a/include/llvm/IR/DebugInfoMetadata.h b/include/llvm/IR/DebugInfoMetadata.h
index 9c5a95721d7..957f807d1ad 100644
--- a/include/llvm/IR/DebugInfoMetadata.h
+++ b/include/llvm/IR/DebugInfoMetadata.h
@@ -574,6 +574,7 @@ public:
   bool isStaticMember() const { return getFlags() & FlagStaticMember; }
   bool isLValueReference() const { return getFlags() & FlagLValueReference; }
   bool isRValueReference() const { return getFlags() & FlagRValueReference; }
+  bool isExternalTypeRef() const { return getFlags() & FlagExternalTypeRef; }
 
   DITypeRef getRef() const { return DITypeRef::get(this); }
 
diff --git a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 7d03a3930d7..45875667027 100644
--- a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -467,7 +467,10 @@ void DwarfDebug::beginModule() {
     for (auto *Ty : CUNode->getRetainedTypes()) {
       // The retained types array by design contains pointers to
       // MDNodes rather than DIRefs. Unique them here.
-      CU.getOrCreateTypeDIE(cast<DIType>(resolve(Ty->getRef())));
+      DIType *RT = cast<DIType>(resolve(Ty->getRef()));
+      if (!RT->isExternalTypeRef())
+        // There is no point in force-emitting a forward declaration.
+        CU.getOrCreateTypeDIE(RT);
     }
     // Emit imported_modules last so that the relevant context is already
     // available.
@@ -1884,7 +1887,7 @@ MCDwarfDwoLineTable *DwarfDebug::getDwoLineTable(const DwarfCompileUnit &CU) {
   return &SplitTypeUnitFileTable;
 }
 
-static uint64_t makeTypeSignature(StringRef Identifier) {
+uint64_t DwarfDebug::makeTypeSignature(StringRef Identifier) {
   MD5 Hash;
   Hash.update(Identifier);
   // ... take the least significant 8 bytes and return those. Our MD5
diff --git a/lib/CodeGen/AsmPrinter/DwarfDebug.h b/lib/CodeGen/AsmPrinter/DwarfDebug.h
index 01f34c6eb81..36502225c29 100644
--- a/lib/CodeGen/AsmPrinter/DwarfDebug.h
+++ b/lib/CodeGen/AsmPrinter/DwarfDebug.h
@@ -544,6 +544,9 @@ public:
   /// Process end of an instruction.
   void endInstruction() override;
 
+  /// Perform an MD5 checksum of \p Identifier and return the lower 64 bits.
+  static uint64_t makeTypeSignature(StringRef Identifier);
+
   /// Add a DIE to the set of types that we're going to pull into
   /// type units.
   void addDwarfTypeUnitType(DwarfCompileUnit &CU, StringRef Identifier,
diff --git a/lib/CodeGen/AsmPrinter/DwarfUnit.cpp b/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
index 355582298e5..799398a8f2f 100644
--- a/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
+++ b/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
@@ -277,6 +277,13 @@ void DwarfUnit::addDIETypeSignature(DIE &Die, const DwarfTypeUnit &Type) {
                dwarf::DW_FORM_ref_sig8, DIETypeSignature(Type));
 }
 
+void DwarfUnit::addDIETypeSignature(DIE &Die, dwarf::Attribute Attribute,
+                                    StringRef Identifier) {
+  uint64_t Signature = DD->makeTypeSignature(Identifier);
+  Die.addValue(DIEValueAllocator, Attribute, dwarf::DW_FORM_ref_sig8,
+               DIEInteger(Signature));
+}
+
 void DwarfUnit::addDIEEntry(DIE &Die, dwarf::Attribute Attribute,
                             DIEEntry Entry) {
   const DIE *DieCU = Die.getUnitOrNull();
@@ -700,7 +707,8 @@ DIE *DwarfUnit::createTypeDIE(const DICompositeType *Ty) {
 
   constructTypeDIE(TyDIE, cast<DICompositeType>(Ty));
 
-  updateAcceleratorTables(Context, Ty, TyDIE);
+  if (!Ty->isExternalTypeRef())
+    updateAcceleratorTables(Context, Ty, TyDIE);
   return &TyDIE;
 }
 
@@ -899,6 +907,13 @@ void DwarfUnit::constructTypeDIE(DIE &Buffer, const DISubroutineType *CTy) {
 }
 
 void DwarfUnit::constructTypeDIE(DIE &Buffer, const DICompositeType *CTy) {
+  if (CTy->isExternalTypeRef()) {
+    StringRef Identifier = CTy->getIdentifier();
+    assert(!Identifier.empty() && "external type ref without identifier");
+    addFlag(Buffer, dwarf::DW_AT_declaration);
+    return addDIETypeSignature(Buffer, dwarf::DW_AT_signature, Identifier);
+  }
+
   // Add name if not anonymous or intermediate type.
   StringRef Name = CTy->getName();
 
diff --git a/lib/CodeGen/AsmPrinter/DwarfUnit.h b/lib/CodeGen/AsmPrinter/DwarfUnit.h
index 44d9d2245dd..28fb71cc462 100644
--- a/lib/CodeGen/AsmPrinter/DwarfUnit.h
+++ b/lib/CodeGen/AsmPrinter/DwarfUnit.h
@@ -228,7 +228,11 @@ public:
   /// Add a DIE attribute data and value.
   void addDIEEntry(DIE &Die, dwarf::Attribute Attribute, DIEEntry Entry);
 
+  /// Add a type's DW_AT_signature and set the  declaration flag.
   void addDIETypeSignature(DIE &Die, const DwarfTypeUnit &Type);
+  /// Add an attribute containing the type signature for a unique identifier.
+  void addDIETypeSignature(DIE &Die, dwarf::Attribute Attribute,
+                           StringRef Identifier);
 
   /// Add block data.
   void addBlock(DIE &Die, dwarf::Attribute Attribute, DIELoc *Block);
diff --git a/lib/IR/DIBuilder.cpp b/lib/IR/DIBuilder.cpp
index 2a90e70af1a..28a8d567c22 100644
--- a/lib/IR/DIBuilder.cpp
+++ b/lib/IR/DIBuilder.cpp
@@ -435,6 +435,18 @@ DISubroutineType *DIBuilder::createSubroutineType(DIFile *File,
   return DISubroutineType::get(VMContext, Flags, ParameterTypes);
 }
 
+DICompositeType *DIBuilder::createExternalTypeRef(unsigned Tag, DIFile *File,
+                                                  StringRef UniqueIdentifier) {
+  assert(!UniqueIdentifier.empty() && "external type ref without uid");
+  auto *CTy =
+      DICompositeType::get(VMContext, Tag, "", nullptr, 0, nullptr, nullptr, 0,
+                           0, 0, DINode::FlagExternalTypeRef, nullptr, 0,
+                           nullptr, nullptr, UniqueIdentifier);
+  // Types with unique IDs need to be in the type map.
+  retainType(CTy);
+  return CTy;
+}
+
 DICompositeType *DIBuilder::createEnumerationType(
     DIScope *Scope, StringRef Name, DIFile *File, unsigned LineNumber,
     uint64_t SizeInBits, uint64_t AlignInBits, DINodeArray Elements,
diff --git a/test/DebugInfo/X86/externaltyperef.ll b/test/DebugInfo/X86/externaltyperef.ll
new file mode 100644
index 00000000000..c344d5f068c
--- /dev/null
+++ b/test/DebugInfo/X86/externaltyperef.ll
@@ -0,0 +1,51 @@
+; REQUIRES: object-emission
+; RUN: %llc_dwarf -filetype=obj -O0 < %s | llvm-dwarfdump -debug-dump=info - | FileCheck %s
+; Manually derived by externalizing the composite types from:
+;
+;   namespace N { class B; }
+;   using N::B;
+;   class A;
+;   A *a;
+;
+; Test the direct use of an external type.
+; CHECK: DW_TAG_variable
+; CHECK:   DW_AT_type [DW_FORM_ref4]	  {{.*}}{[[PTR:.*]]}
+; CHECK: [[PTR]]: DW_TAG_pointer_type
+; CHECK:   DW_AT_type [DW_FORM_ref4]  	  {{.*}}{[[A:.*]]}
+; CHECK: [[A]]: DW_TAG_class_type
+; CHECK:   DW_AT_declaration [DW_FORM_flag]	(0x01)
+; CHECK:   DW_AT_signature [DW_FORM_ref_sig8]	(0x4e834ea939695c24)
+; CHECK: [[B:.*]]: DW_TAG_class_type
+; CHECK:   DW_AT_declaration [DW_FORM_flag]	(0x01)
+; CHECK:   DW_AT_signature [DW_FORM_ref_sig8]	(0x942e51c7addda5f7)
+; CHECK:   DW_TAG_imported_declaration
+; CHECK:     DW_AT_import [DW_FORM_ref4]  {{.*}}[[B]]
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.10.0"
+
+%class.A = type opaque
+
+@a = global %class.A* null, align 8
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!13, !14, !15}
+!llvm.ident = !{!16}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 3.7.0 (trunk 242039) (llvm/trunk 242046)", isOptimized: false, runtimeVersion: 0, emissionKind: 1, enums: !2, retainedTypes: !3, globals: !5, imports: !11)
+!1 = !DIFile(filename: "test.cpp", directory: "/")
+!2 = !{}
+!3 = !{!4, !9}
+!4 = !DICompositeType(tag: DW_TAG_class_type, name: "A", file: !1, flags: DIFlagExternalTypeRef, identifier: "_ZTS1A")
+!5 = !{!6}
+!6 = !DIGlobalVariable(name: "a", scope: !0, file: !1, line: 2, type: !7, isLocal: false, isDefinition: true, variable: %class.A** @a)
+!7 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !"_ZTS1A", size: 64, align: 64)
+!8 = !DICompositeType(tag: DW_TAG_class_type, name: "B", file: !1, flags: DIFlagExternalTypeRef, identifier: "_ZTS1B")
+!9 = !DICompositeType(tag: DW_TAG_class_type, name: "A", file: !1, flags: DIFlagExternalTypeRef, identifier: "_ZTSN1N1BE")
+!10 = !DINamespace(name: "N", scope: null, file: !1, line: 1)
+!11 = !{!12}
+!12 = !DIImportedEntity(tag: DW_TAG_imported_declaration, scope: !0, entity: !"_ZTSN1N1BE", line: 4)
+!13 = !{i32 2, !"Dwarf Version", i32 2}
+!14 = !{i32 2, !"Debug Info Version", i32 3}
+!15 = !{i32 1, !"PIC Level", i32 2}
+!16 = !{!"clang version 3.7.0 (trunk 242039) (llvm/trunk 242046)"}