diff --git a/src/clang_tu.cc b/src/clang_tu.cc
index 5042714f0..131adcc05 100644
--- a/src/clang_tu.cc
+++ b/src/clang_tu.cc
@@ -27,6 +27,13 @@ std::string pathFromFileEntry(const FileEntry &file) {
   return normalizeFolder(ret) ? ret : realPath(ret);
 }
 
+bool isInsideMainFile(const SourceManager &sm, SourceLocation sl) {
+  if (!sl.isValid())
+    return false;
+  FileID fid = sm.getFileID(sm.getExpansionLoc(sl));
+  return fid == sm.getMainFileID() || fid == sm.getPreambleFileID();
+}
+
 static Pos decomposed2LineAndCol(const SourceManager &sm,
                                  std::pair<FileID, unsigned> i) {
   int l = (int)sm.getLineNumber(i.first, i.second) - 1,
diff --git a/src/clang_tu.hh b/src/clang_tu.hh
index b53799a88..b37950926 100644
--- a/src/clang_tu.hh
+++ b/src/clang_tu.hh
@@ -20,6 +20,8 @@ namespace vfs = clang::vfs;
 namespace ccls {
 std::string pathFromFileEntry(const clang::FileEntry &file);
 
+bool isInsideMainFile(const clang::SourceManager &sm, clang::SourceLocation sl);
+
 Range fromCharSourceRange(const clang::SourceManager &sm,
                           const clang::LangOptions &lang,
                           clang::CharSourceRange csr,
diff --git a/src/sema_manager.cc b/src/sema_manager.cc
index 6a228f391..1002565b7 100644
--- a/src/sema_manager.cc
+++ b/src/sema_manager.cc
@@ -243,7 +243,7 @@ class StoreDiags : public DiagnosticConsumer {
       return;
     const SourceManager &sm = info.getSourceManager();
     StringRef filename = sm.getFilename(info.getLocation());
-    bool concerned = sm.isWrittenInMainFile(l);
+    bool concerned = isInsideMainFile(sm, l);
     auto fillDiagBase = [&](DiagBase &d) {
       llvm::SmallString<64> message;
       info.FormatDiagnostic(message);