diff --git a/clang-tools-extra/clangd/XRefs.cpp b/clang-tools-extra/clangd/XRefs.cpp
--- a/clang-tools-extra/clangd/XRefs.cpp
+++ b/clang-tools-extra/clangd/XRefs.cpp
@@ -299,7 +299,7 @@
                                             RelationKind Predicate,
                                             const SymbolIndex *Index,
                                             llvm::StringRef MainFilePath) {
-  if (IDs.empty())
+  if (IDs.empty() || !Index)
     return {};
   static constexpr trace::Metric FindImplementorsMetric(
       "find_implementors", trace::Metric::Counter, "case");