diff --git a/clang-tools-extra/clangd/ClangdLSPServer.h b/clang-tools-extra/clangd/ClangdLSPServer.h
--- a/clang-tools-extra/clangd/ClangdLSPServer.h
+++ b/clang-tools-extra/clangd/ClangdLSPServer.h
@@ -44,6 +44,7 @@
                   llvm::Optional<Path> CompileCommandsDir, bool UseDirBasedCDB,
                   llvm::Optional<OffsetEncoding> ForcedOffsetEncoding,
                   const ClangdServer::Options &Opts);
+  /// The destructor blocks on any outstanding background tasks.
   ~ClangdLSPServer();
 
   /// Run LSP server loop, communicating with the Transport provided in the
@@ -211,11 +212,11 @@
   std::unique_ptr<GlobalCompilationDatabase> BaseCDB;
   // CDB is BaseCDB plus any comands overridden via LSP extensions.
   llvm::Optional<OverlayCDB> CDB;
-  // The ClangdServer is created by the "initialize" LSP method.
-  // It is destroyed before run() returns, to ensure worker threads exit.
   ClangdServer::Options ClangdServerOpts;
-  llvm::Optional<ClangdServer> Server;
   llvm::Optional<OffsetEncoding> NegotiatedOffsetEncoding;
+  // The ClangdServer is created by the "initialize" LSP method. It should be
+  // destroyed first, to ensure worker threads don't access other members.
+  llvm::Optional<ClangdServer> Server;
 };
 } // namespace clangd
 } // namespace clang
diff --git a/clang-tools-extra/clangd/ClangdLSPServer.cpp b/clang-tools-extra/clangd/ClangdLSPServer.cpp
--- a/clang-tools-extra/clangd/ClangdLSPServer.cpp
+++ b/clang-tools-extra/clangd/ClangdLSPServer.cpp
@@ -1241,8 +1241,6 @@
     CleanExit = false;
   }
 
-  // Destroy ClangdServer to ensure all worker threads finish.
-  Server.reset();
   return CleanExit && ShutdownRequestReceived;
 }
 
diff --git a/clang-tools-extra/clangd/tool/ClangdMain.cpp b/clang-tools-extra/clangd/tool/ClangdMain.cpp
--- a/clang-tools-extra/clangd/tool/ClangdMain.cpp
+++ b/clang-tools-extra/clangd/tool/ClangdMain.cpp
@@ -27,6 +27,7 @@
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/TargetSelect.h"
 #include "llvm/Support/raw_ostream.h"
+#include <chrono>
 #include <cstdlib>
 #include <iostream>
 #include <memory>
@@ -670,6 +671,24 @@
       /*UseDirBasedCDB=*/CompileArgsFrom == FilesystemCompileArgs,
       OffsetEncodingFromFlag, Opts);
   llvm::set_thread_name("clangd.main");
-  return LSPServer.run() ? 0
-                         : static_cast<int>(ErrorResultCode::NoShutdownRequest);
+  int ExitCode = LSPServer.run()
+                     ? 0
+                     : static_cast<int>(ErrorResultCode::NoShutdownRequest);
+  log("LSP finished, exiting with status {0}", ExitCode);
+
+  // There may still be lingering background threads (e.g. slow requests
+  // whose results will be dropped, background index shutting down).
+  //
+  // These should terminate quickly, and ~ClangdLSPServer blocks on them.
+  // However if a bug causes them to run forever, we want to ensure the process
+  // eventually exits. As clangd isn't directly user-facing, an editor can
+  // "leak" clangd processes. Crashing in this case contains the damage.
+  //
+  // This is more portable than sys::WatchDog, and yields a stack trace.
+  std::thread([] {
+    std::this_thread::sleep_for(std::chrono::minutes(5));
+    std::abort();
+  }).detach();
+
+  return ExitCode;
 }