diff --git a/clang-tools-extra/clangd/ClangdServer.h b/clang-tools-extra/clangd/ClangdServer.h
--- a/clang-tools-extra/clangd/ClangdServer.h
+++ b/clang-tools-extra/clangd/ClangdServer.h
@@ -362,6 +362,7 @@
   Context createProcessingContext(PathRef) const;
   config::Provider *ConfigProvider = nullptr;
 
+  const GlobalCompilationDatabase &CDB;
   const ThreadsafeFS &TFS;
   Callbacks *ServerCallbacks = nullptr;
   mutable std::mutex ConfigDiagnosticsMu;
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
@@ -139,7 +139,8 @@
 ClangdServer::ClangdServer(const GlobalCompilationDatabase &CDB,
                            const ThreadsafeFS &TFS, const Options &Opts,
                            Callbacks *Callbacks)
-    : ConfigProvider(Opts.ConfigProvider), TFS(TFS), ServerCallbacks(Callbacks),
+    : ConfigProvider(Opts.ConfigProvider), CDB(CDB), TFS(TFS),
+      ServerCallbacks(Callbacks),
       DynamicIdx(Opts.BuildDynamicSymbolIndex
                      ? new FileIndex(Opts.HeavyweightDynamicSymbolIndex,
                                      Opts.CollectMainFileRefs)
@@ -873,6 +874,7 @@
 LLVM_NODISCARD bool
 ClangdServer::blockUntilIdleForTest(llvm::Optional<double> TimeoutSeconds) {
   return WorkScheduler.blockUntilIdle(timeoutSeconds(TimeoutSeconds)) &&
+         CDB.blockUntilIdle(timeoutSeconds(TimeoutSeconds)) &&
          (!BackgroundIdx ||
           BackgroundIdx->blockUntilIdleForTest(TimeoutSeconds));
 }
diff --git a/clang-tools-extra/clangd/GlobalCompilationDatabase.h b/clang-tools-extra/clangd/GlobalCompilationDatabase.h
--- a/clang-tools-extra/clangd/GlobalCompilationDatabase.h
+++ b/clang-tools-extra/clangd/GlobalCompilationDatabase.h
@@ -51,6 +51,10 @@
   /// Clangd should treat the results as unreliable.
   virtual tooling::CompileCommand getFallbackCommand(PathRef File) const;
 
+  /// If the CDB does any asynchronous work, wait for it to complete.
+  /// For use in tests.
+  virtual bool blockUntilIdle(Deadline D) const { return true; }
+
   using CommandChanged = Event<std::vector<std::string>>;
   /// The callback is notified when files may have new compile commands.
   /// The argument is a list of full file paths.
@@ -75,6 +79,8 @@
 
   tooling::CompileCommand getFallbackCommand(PathRef File) const override;
 
+  bool blockUntilIdle(Deadline D) const override;
+
 private:
   const GlobalCompilationDatabase *Base;
   std::unique_ptr<GlobalCompilationDatabase> BaseOwner;
diff --git a/clang-tools-extra/clangd/GlobalCompilationDatabase.cpp b/clang-tools-extra/clangd/GlobalCompilationDatabase.cpp
--- a/clang-tools-extra/clangd/GlobalCompilationDatabase.cpp
+++ b/clang-tools-extra/clangd/GlobalCompilationDatabase.cpp
@@ -635,5 +635,11 @@
   return Base->getFallbackCommand(File);
 }
 
+bool DelegatingCDB::blockUntilIdle(Deadline D) const {
+  if (!Base)
+    return true;
+  return Base->blockUntilIdle(D);
+}
+
 } // namespace clangd
 } // namespace clang