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
@@ -894,6 +894,14 @@
       FileInputs = Inputs;
     }
 
+    if (isCancelled()) {
+      log("ASTWorker skipping update {0} for file {1}", Inputs.Version,
+          FileName);
+      // Don't even emplace a preamble, as we still want the first valid update
+      // to block any further reads.
+      return;
+    }
+
     log("ASTWorker building file {0} version {1} with command {2}\n[{3}]\n{4}",
         FileName, Inputs.Version, Inputs.CompileCommand.Heuristic,
         Inputs.CompileCommand.Directory,