Index: include/clang/AST/ExternalASTMerger.h
===================================================================
--- include/clang/AST/ExternalASTMerger.h
+++ include/clang/AST/ExternalASTMerger.h
@@ -44,6 +44,8 @@
   FindExternalLexicalDecls(const DeclContext *DC,
                            llvm::function_ref<bool(Decl::Kind)> IsKindWeWant,
                            SmallVectorImpl<Decl *> &Result) override;
+
+   void CompleteType(TagDecl *Tag) override;
 };
 
 } // end namespace clang
Index: lib/AST/ASTImporter.cpp
===================================================================
--- lib/AST/ASTImporter.cpp
+++ lib/AST/ASTImporter.cpp
@@ -1622,10 +1622,18 @@
 
   // We may already have a record of the same name; try to find and match it.
   RecordDecl *AdoptDecl = nullptr;
+  RecordDecl *PrevDecl = nullptr;
   if (!DC->isFunctionOrMethod()) {
     SmallVector<NamedDecl *, 4> ConflictingDecls;
     SmallVector<NamedDecl *, 2> FoundDecls;
     DC->getRedeclContext()->localUncachedLookup(SearchName, FoundDecls);
+
+    if (!FoundDecls.empty()) {
+      // We're going to have to compare D against potentially conflicting Decls, so complete it.
+      if (D->hasExternalLexicalStorage() && !D->isCompleteDefinition())
+        D->getASTContext().getExternalSource()->CompleteType(D);
+    }
+
     for (unsigned I = 0, N = FoundDecls.size(); I != N; ++I) {
       if (!FoundDecls[I]->isInIdentifierNamespace(IDNS))
         continue;
@@ -1652,6 +1660,8 @@
           }
         }
 
+        PrevDecl = FoundRecord;
+
         if (RecordDecl *FoundDef = FoundRecord->getDefinition()) {
           if ((SearchName && !D->isCompleteDefinition())
               || (D->isCompleteDefinition() &&
@@ -1744,6 +1754,9 @@
     LexicalDC->addDeclInternal(D2);
     if (D->isAnonymousStructOrUnion())
       D2->setAnonymousStructOrUnion(true);
+    if (PrevDecl) {
+      D2->setPreviousDecl(PrevDecl);
+    }
   }
   
   Importer.Imported(D, D2);
Index: lib/AST/ASTStructuralEquivalence.cpp
===================================================================
--- lib/AST/ASTStructuralEquivalence.cpp
+++ lib/AST/ASTStructuralEquivalence.cpp
@@ -855,6 +855,11 @@
 
   if (CXXRecordDecl *D1CXX = dyn_cast<CXXRecordDecl>(D1)) {
     if (CXXRecordDecl *D2CXX = dyn_cast<CXXRecordDecl>(D2)) {
+      if (D1CXX->hasExternalLexicalStorage() &&
+          !D1CXX->isCompleteDefinition()) {
+        D1CXX->getASTContext().getExternalSource()->CompleteType(D1CXX);
+      }
+
       if (D1CXX->getNumBases() != D2CXX->getNumBases()) {
         if (Context.Complain) {
           Context.Diag2(D2->getLocation(), diag::warn_odr_tag_type_inconsistent)
Index: lib/AST/ExternalASTMerger.cpp
===================================================================
--- lib/AST/ExternalASTMerger.cpp
+++ lib/AST/ExternalASTMerger.cpp
@@ -178,3 +178,9 @@
         }
       });
 }
+
+void ExternalASTMerger::CompleteType(TagDecl *Tag) {
+  SmallVector<Decl *, 0> Result;
+  FindExternalLexicalDecls(Tag, [](Decl::Kind) { return true; }, Result);
+  Tag->setHasExternalLexicalStorage(false);
+}
Index: test/Import/conflicting-struct/Inputs/S1.cpp
===================================================================
--- /dev/null
+++ test/Import/conflicting-struct/Inputs/S1.cpp
@@ -0,0 +1,6 @@
+class T;
+
+class S {
+  T *t;
+  int a;
+};
Index: test/Import/conflicting-struct/Inputs/S2.cpp
===================================================================
--- /dev/null
+++ test/Import/conflicting-struct/Inputs/S2.cpp
@@ -0,0 +1,7 @@
+class U {
+  int b;
+};
+
+class T {
+  U u;
+};
Index: test/Import/conflicting-struct/test.cpp
===================================================================
--- /dev/null
+++ test/Import/conflicting-struct/test.cpp
@@ -0,0 +1,7 @@
+// RUN: clang-import-test --import %S/Inputs/S1.cpp --import %S/Inputs/S2.cpp -expression %s
+void expr() {
+  S MyS;
+  T MyT;
+  MyS.a = 3;
+  MyT.u.b = 2;
+}
Index: tools/clang-import-test/clang-import-test.cpp
===================================================================
--- tools/clang-import-test/clang-import-test.cpp
+++ tools/clang-import-test/clang-import-test.cpp
@@ -42,6 +42,10 @@
     Imports("import", llvm::cl::ZeroOrMore,
             llvm::cl::desc("Path to a file containing declarations to import"));
 
+static llvm::cl::opt<bool>
+    Direct("direct", llvm::cl::Optional,
+             llvm::cl::desc("Use the parsed declarations without indirection"));
+
 static llvm::cl::list<std::string>
     ClangArgs("Xcc", llvm::cl::ZeroOrMore,
               llvm::cl::desc("Argument to pass to the CompilerInvocation"),
@@ -172,6 +176,14 @@
   return Ins;
 }
 
+std::unique_ptr<CompilerInstance>
+BuildCompilerInstance(ArrayRef<std::string> ClangArgs) {
+  std::vector<const char *> ClangArgv(ClangArgs.size());
+  std::transform(ClangArgs.begin(), ClangArgs.end(), ClangArgv.begin(),
+                 [](const std::string &s) -> const char * { return s.data(); });
+  return init_convenience::BuildCompilerInstance(ClangArgv);
+}
+
 std::unique_ptr<ASTContext>
 BuildASTContext(CompilerInstance &CI, SelectorTable &ST, Builtin::Context &BC) {
   auto AST = llvm::make_unique<ASTContext>(
@@ -205,6 +217,21 @@
   CI.getASTContext().getTranslationUnitDecl()->setHasExternalVisibleStorage();
 }
 
+std::unique_ptr<CompilerInstance> BuildIndirect(std::unique_ptr<CompilerInstance> &CI) {
+  std::vector<const char *> ClangArgv(ClangArgs.size());
+  std::transform(ClangArgs.begin(), ClangArgs.end(), ClangArgv.begin(),
+                 [](const std::string &s) -> const char * { return s.data(); });
+  std::unique_ptr<CompilerInstance> IndirectCI =
+      init_convenience::BuildCompilerInstance(ClangArgv);
+  auto ST = llvm::make_unique<SelectorTable>();
+  auto BC = llvm::make_unique<Builtin::Context>();
+  std::unique_ptr<ASTContext> AST =
+      init_convenience::BuildASTContext(*IndirectCI, *ST, *BC);
+  IndirectCI->setASTContext(AST.release());
+  AddExternalSource(*IndirectCI, CI);
+  return IndirectCI;
+}
+
 llvm::Error ParseSource(const std::string &Path, CompilerInstance &CI,
                         CodeGenerator &CG) {
   SourceManager &SM = CI.getSourceManager();
@@ -231,7 +258,9 @@
   std::unique_ptr<ASTContext> AST =
       init_convenience::BuildASTContext(*CI, *ST, *BC);
   CI->setASTContext(AST.release());
-  AddExternalSource(*CI, Imports);
+  if (Imports.size()) {
+    AddExternalSource(*CI, Imports);
+  }
 
   auto LLVMCtx = llvm::make_unique<llvm::LLVMContext>();
   std::unique_ptr<CodeGenerator> CG =
@@ -268,8 +297,21 @@
       ImportCIs.push_back(std::move(*ImportCI));
     }
   }
+  std::vector<std::unique_ptr<CompilerInstance>> IndirectCIs;
+  if (!Direct) {
+    for (auto &ImportCI : ImportCIs) {
+      llvm::Expected<std::unique_ptr<CompilerInstance>> IndirectCI =
+          BuildIndirect(ImportCI);
+      if (auto E = IndirectCI.takeError()) {
+        llvm::errs() << llvm::toString(std::move(E));
+        exit(-1);
+      } else {
+        IndirectCIs.push_back(std::move(*IndirectCI));
+      }
+    }
+  }
   llvm::Expected<std::unique_ptr<CompilerInstance>> ExpressionCI =
-      Parse(Expression, ImportCIs);
+      Parse(Expression, Direct ? ImportCIs : IndirectCIs);
   if (auto E = ExpressionCI.takeError()) {
     llvm::errs() << llvm::toString(std::move(E));
     exit(-1);
@@ -277,3 +319,4 @@
     return 0;
   }
 }
+