Index: lib/AST/ASTDiagnostic.cpp
===================================================================
--- lib/AST/ASTDiagnostic.cpp
+++ lib/AST/ASTDiagnostic.cpp
@@ -420,6 +420,8 @@
         OS << ConvertTypeToDiagnosticString(Context,
                                             Context.getTypeDeclType(Type),
                                             PrevArgs, QualTypeVals);
+      } else if (const auto *LS = dyn_cast<LinkageSpecDecl>(DC)) {
+        OS << "linkage specification";
       } else {
         assert(isa<NamedDecl>(DC) && "Expected a NamedDecl");
         NamedDecl *ND = cast<NamedDecl>(DC);
Index: test/SemaCXX/warn-shadow.cpp
===================================================================
--- test/SemaCXX/warn-shadow.cpp
+++ test/SemaCXX/warn-shadow.cpp
@@ -206,3 +206,10 @@
 }
 
 }
+
+extern "C" {
+typedef int externC; // expected-note {{previous declaration is here}}
+}
+void handleLinkageSpec() {
+  typedef void externC; // expected-warning {{declaration shadows a typedef in linkage specification}}
+}