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
@@ -13,6 +13,9 @@
 #include "Protocol.h"
 #include "Transport.h"
 #include "index/Background.h"
+#include "index/Index.h"
+#include "index/Merge.h"
+#include "index/ProjectAware.h"
 #include "index/Serialization.h"
 #include "index/remote/Client.h"
 #include "refactor/Rename.h"
@@ -40,6 +43,7 @@
 #include <mutex>
 #include <string>
 #include <thread>
+#include <vector>
 
 #ifndef _WIN32
 #include <unistd.h>
@@ -726,6 +730,7 @@
     Opts.ResourceDir = ResourceDir;
   Opts.BuildDynamicSymbolIndex = EnableIndex;
   Opts.CollectMainFileRefs = CollectMainFileRefs;
+  std::vector<std::unique_ptr<SymbolIndex>> IdxStack;
   std::unique_ptr<SymbolIndex> StaticIdx;
   std::future<void> AsyncIndexLoad; // Block exit while loading the index.
   if (EnableIndex && !IndexFile.empty()) {
@@ -757,7 +762,15 @@
   }
 #endif
   Opts.BackgroundIndex = EnableBackgroundIndex;
-  Opts.StaticIndex = StaticIdx.get();
+  ProjectAwareIndex PAI;
+  if (StaticIdx) {
+    IdxStack.emplace_back(std::move(StaticIdx));
+    IdxStack.emplace_back(
+        std::make_unique<MergedIndex>(&PAI, IdxStack.back().get()));
+    Opts.StaticIndex = IdxStack.back().get();
+  } else {
+    Opts.StaticIndex = &PAI;
+  }
   Opts.AsyncThreadsCount = WorkerThreadsCount;
   Opts.BuildRecoveryAST = RecoveryAST;
   Opts.PreserveRecoveryASTType = RecoveryASTType;