diff --git a/clang-tools-extra/clangd/ClangdServer.cpp b/clang-tools-extra/clangd/ClangdServer.cpp
--- a/clang-tools-extra/clangd/ClangdServer.cpp
+++ b/clang-tools-extra/clangd/ClangdServer.cpp
@@ -75,8 +75,6 @@
                      const CanonicalIncludes &CanonIncludes) override {
     if (FIndex)
       FIndex->updatePreamble(Path, Version, Ctx, std::move(PP), CanonIncludes);
-    if (ServerCallbacks)
-      ServerCallbacks->onSemanticsMaybeChanged(Path);
   }
 
   void onMainAST(PathRef Path, ParsedAST &AST, PublishFn Publish) override {
@@ -105,6 +103,11 @@
       ServerCallbacks->onFileUpdated(File, Status);
   }
 
+  void onPreamblePublished(PathRef File) override {
+    if (ServerCallbacks)
+      ServerCallbacks->onSemanticsMaybeChanged(File);
+  }
+
 private:
   FileIndex *FIndex;
   ClangdServer::Callbacks *ServerCallbacks;
diff --git a/clang-tools-extra/clangd/TUScheduler.h b/clang-tools-extra/clangd/TUScheduler.h
--- a/clang-tools-extra/clangd/TUScheduler.h
+++ b/clang-tools-extra/clangd/TUScheduler.h
@@ -169,6 +169,11 @@
 
   /// Called whenever the TU status is updated.
   virtual void onFileUpdated(PathRef File, const TUStatus &Status) {}
+
+  /// Preamble for the TU have changed. This might imply new semantics (e.g.
+  /// different highlightings). Any actions on the file are guranteed to see new
+  /// preamble after the callback.
+  virtual void onPreamblePublished(PathRef File) {}
 };
 
 /// Handles running tasks for ClangdServer and managing the resources (e.g.,
diff --git a/clang-tools-extra/clangd/TUScheduler.cpp b/clang-tools-extra/clangd/TUScheduler.cpp
--- a/clang-tools-extra/clangd/TUScheduler.cpp
+++ b/clang-tools-extra/clangd/TUScheduler.cpp
@@ -909,6 +909,7 @@
     ASTPeer.updatePreamble(std::move(Req.CI), std::move(Req.Inputs),
                            LatestBuild, std::move(Req.CIDiags),
                            std::move(Req.WantDiags));
+    Callbacks.onPreamblePublished(FileName);
   });
 
   if (!LatestBuild || Inputs.ForceRebuild) {