Index: clang-tools-extra/clang-tidy/modernize/UseUsingCheck.cpp
===================================================================
--- clang-tools-extra/clang-tidy/modernize/UseUsingCheck.cpp
+++ clang-tools-extra/clang-tidy/modernize/UseUsingCheck.cpp
@@ -48,6 +48,9 @@
   if (StartLoc.isMacroID() && IgnoreMacros)
     return;
 
+  if (MatchedDecl->getDeclContext()->isExternCContext())
+    return;
+
   static const char *UseUsingWarning = "use 'using' instead of 'typedef'";
 
   // Warn at StartLoc but do not fix if there is macro or array.
Index: clang-tools-extra/test/clang-tidy/checkers/modernize-use-using.cpp
===================================================================
--- clang-tools-extra/test/clang-tidy/checkers/modernize-use-using.cpp
+++ clang-tools-extra/test/clang-tidy/checkers/modernize-use-using.cpp
@@ -278,3 +278,7 @@
 // CHECK-MESSAGES: :[[@LINE-1]]:1: warning: use 'using' instead of 'typedef'
 // CHECK-FIXES: using EnumT2_CheckTypedefImpactFromAnotherFile = enum { ea2, eb2 };
 
+extern "C" {
+typedef int Type;
+// No messages expected, since this code may be shared verbatim with C.
+}