diff --git a/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.cpp b/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.cpp
index a71813a103df3..c35f0b941c600 100644
--- a/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.cpp
+++ b/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.cpp
@@ -358,8 +358,27 @@ getFixIt(const tooling::Diagnostic &Diagnostic, bool AnyFix) {
 
 } // namespace clang::tidy
 
+void ClangTidyDiagnosticConsumer::BeginSourceFile(const LangOptions &LangOpts,
+                                                  const Preprocessor *PP) {
+  DiagnosticConsumer::BeginSourceFile(LangOpts, PP);
+
+  assert(!InSourceFile);
+  InSourceFile = true;
+}
+
+void ClangTidyDiagnosticConsumer::EndSourceFile() {
+  assert(InSourceFile);
+  InSourceFile = false;
+
+  DiagnosticConsumer::EndSourceFile();
+}
+
 void ClangTidyDiagnosticConsumer::HandleDiagnostic(
     DiagnosticsEngine::Level DiagLevel, const Diagnostic &Info) {
+  // A diagnostic should not be reported outside of a
+  // BeginSourceFile()/EndSourceFile() pair if it has a source location.
+  assert(InSourceFile || Info.getLocation().isInvalid());
+
   if (LastErrorWasIgnored && DiagLevel == DiagnosticsEngine::Note)
     return;
 
diff --git a/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.h b/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.h
index a8851e794f24b..e8887a3fe2bf8 100644
--- a/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.h
+++ b/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.h
@@ -292,6 +292,11 @@ class ClangTidyDiagnosticConsumer : public DiagnosticConsumer {
   void HandleDiagnostic(DiagnosticsEngine::Level DiagLevel,
                         const Diagnostic &Info) override;
 
+  void BeginSourceFile(const LangOptions &LangOpts,
+                       const Preprocessor *PP = nullptr) override;
+
+  void EndSourceFile() override;
+
   // Retrieve the diagnostics that were captured.
   std::vector<ClangTidyError> take();
 
@@ -326,6 +331,7 @@ class ClangTidyDiagnosticConsumer : public DiagnosticConsumer {
   bool LastErrorRelatesToUserCode = false;
   bool LastErrorPassesLineFilter = false;
   bool LastErrorWasIgnored = false;
+  bool InSourceFile = false;
 };
 
 } // end namespace tidy
diff --git a/clang/lib/Frontend/FrontendAction.cpp b/clang/lib/Frontend/FrontendAction.cpp
index ef7ae27a2694a..f5996a8e1e88b 100644
--- a/clang/lib/Frontend/FrontendAction.cpp
+++ b/clang/lib/Frontend/FrontendAction.cpp
@@ -1243,13 +1243,15 @@ llvm::Error FrontendAction::Execute() {
 void FrontendAction::EndSourceFile() {
   CompilerInstance &CI = getCompilerInstance();
 
-  // Inform the diagnostic client we are done with this source file.
-  CI.getDiagnosticClient().EndSourceFile();
-
   // Inform the preprocessor we are done.
   if (CI.hasPreprocessor())
     CI.getPreprocessor().EndSourceFile();
 
+  // Inform the diagnostic client we are done with this source file.
+  // Do this after notifying the preprocessor, so that end-of-file preprocessor
+  // callbacks can report diagnostics.
+  CI.getDiagnosticClient().EndSourceFile();
+
   // Finalize the action.
   EndSourceFileAction();