diff --git a/clang-tools-extra/clangd/ClangdServer.cpp b/clang-tools-extra/clangd/ClangdServer.cpp
index 763fea68360ac..cbcc90258f34e 100644
--- a/clang-tools-extra/clangd/ClangdServer.cpp
+++ b/clang-tools-extra/clangd/ClangdServer.cpp
@@ -93,7 +93,7 @@ struct UpdateIndexCallbacks : public ParsingCallbacks {
                              ASTCtx.getPreprocessor(), *CanonIncludes);
     };
 
-    if (Tasks) {
+    if (Opts.AsyncPreambleIndexing && Tasks) {
       Tasks->runAsync("Preamble indexing for:" + Path + Version,
                       std::move(Task));
     } else
diff --git a/clang-tools-extra/clangd/ClangdServer.h b/clang-tools-extra/clangd/ClangdServer.h
index 2bc8f02ff38a4..88b6d2f11d9a0 100644
--- a/clang-tools-extra/clangd/ClangdServer.h
+++ b/clang-tools-extra/clangd/ClangdServer.h
@@ -185,6 +185,10 @@ class ClangdServer {
     /// regions in the document.
     bool PublishInactiveRegions = false;
 
+    /// Whether to run preamble indexing asynchronously in an independent
+    /// thread.
+    bool AsyncPreambleIndexing = false;
+
     explicit operator TUScheduler::Options() const;
   };
   // Sensible default options for use in tests.