Index: clang-tools-extra/clang-tidy/ClangTidy.cpp
===================================================================
--- clang-tools-extra/clang-tidy/ClangTidy.cpp
+++ clang-tools-extra/clang-tidy/ClangTidy.cpp
@@ -615,6 +615,8 @@
   TUD.MainSourceFile = std::string(MainFilePath);
   for (const auto &Error : Errors) {
     tooling::Diagnostic Diag = Error;
+    if (Error.IsWarningAsError)
+      Diag.DiagLevel = tooling::Diagnostic::Error;
     TUD.Diagnostics.insert(TUD.Diagnostics.end(), Diag);
   }
 
Index: clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.cpp
===================================================================
--- clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.cpp
+++ clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.cpp
@@ -421,8 +421,6 @@
 
     bool IsWarningAsError = DiagLevel == DiagnosticsEngine::Warning &&
                             Context.treatAsError(CheckName);
-    if (IsWarningAsError)
-      Level = ClangTidyError::Error;
     Errors.emplace_back(CheckName, Level, Context.getCurrentBuildDirectory(),
                         IsWarningAsError);
   }