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
@@ -271,9 +271,13 @@
     if (!IP)
       return CB(IP.takeError());
 
-    auto PreambleData = IP->Preamble;
-    CB(clangd::signatureHelp(File, IP->Command, PreambleData, IP->Contents, Pos,
-                             FS, Index));
+    const auto *PreambleData = IP->Preamble;
+    if (!PreambleData)
+      return CB(llvm::createStringError(llvm::inconvertibleErrorCode(),
+                                        "Failed to parse includes"));
+
+    CB(clangd::signatureHelp(File, IP->Command, *PreambleData, IP->Contents,
+                             Pos, FS, Index));
   };
 
   // Unlike code completion, we wait for an up-to-date preamble here.
diff --git a/clang-tools-extra/clangd/CodeComplete.h b/clang-tools-extra/clangd/CodeComplete.h
--- a/clang-tools-extra/clangd/CodeComplete.h
+++ b/clang-tools-extra/clangd/CodeComplete.h
@@ -276,7 +276,7 @@
 /// Get signature help at a specified \p Pos in \p FileName.
 SignatureHelp signatureHelp(PathRef FileName,
                             const tooling::CompileCommand &Command,
-                            const PreambleData *Preamble, StringRef Contents,
+                            const PreambleData &Preamble, StringRef Contents,
                             Position Pos,
                             IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS,
                             const SymbolIndex *Index);
diff --git a/clang-tools-extra/clangd/CodeComplete.cpp b/clang-tools-extra/clangd/CodeComplete.cpp
--- a/clang-tools-extra/clangd/CodeComplete.cpp
+++ b/clang-tools-extra/clangd/CodeComplete.cpp
@@ -1022,7 +1022,7 @@
 struct SemaCompleteInput {
   PathRef FileName;
   const tooling::CompileCommand &Command;
-  const PreambleData *Preamble;
+  const PreambleData &Preamble;
   llvm::StringRef Contents;
   size_t Offset;
   llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS;
@@ -1054,8 +1054,8 @@
                       IncludeStructure *Includes = nullptr) {
   trace::Span Tracer("Sema completion");
   llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS = Input.VFS;
-  if (Input.Preamble && Input.Preamble->StatCache)
-    VFS = Input.Preamble->StatCache->getConsumingFS(std::move(VFS));
+  if (Input.Preamble.StatCache)
+    VFS = Input.Preamble.StatCache->getConsumingFS(std::move(VFS));
   ParseInputs ParseInput;
   ParseInput.CompileCommand = Input.Command;
   ParseInput.FS = VFS;
@@ -1099,9 +1099,7 @@
   // NOTE: we must call BeginSourceFile after prepareCompilerInstance. Otherwise
   // the remapped buffers do not get freed.
   auto Clang = prepareCompilerInstance(
-      std::move(CI),
-      (Input.Preamble && !CompletingInPreamble) ? &Input.Preamble->Preamble
-                                                : nullptr,
+      std::move(CI), !CompletingInPreamble ? &Input.Preamble.Preamble : nullptr,
       std::move(ContentsBuffer), std::move(VFS), IgnoreDiags);
   Clang->getPreprocessorOpts().SingleFileParseMode = CompletingInPreamble;
   Clang->setCodeCompletionConsumer(Consumer.release());
@@ -1118,8 +1116,7 @@
   //  - but Sema code complete won't see them: as part of the preamble, they're
   //    deserialized only when mentioned.
   // Force them to be deserialized so SemaCodeComplete sees them.
-  if (Input.Preamble)
-    loadMainFilePreambleMacros(Clang->getPreprocessor(), *Input.Preamble);
+  loadMainFilePreambleMacros(Clang->getPreprocessor(), Input.Preamble);
   if (Includes)
     Clang->getPreprocessor().addPPCallbacks(
         collectIncludeStructureCallback(Clang->getSourceManager(), Includes));
@@ -1758,12 +1755,12 @@
   return (!Preamble || Opts.RunParser == CodeCompleteOptions::NeverParse)
              ? std::move(Flow).runWithoutSema(Contents, *Offset, VFS)
              : std::move(Flow).run(
-                   {FileName, Command, Preamble, Contents, *Offset, VFS});
+                   {FileName, Command, *Preamble, Contents, *Offset, VFS});
 }
 
 SignatureHelp signatureHelp(PathRef FileName,
                             const tooling::CompileCommand &Command,
-                            const PreambleData *Preamble,
+                            const PreambleData &Preamble,
                             llvm::StringRef Contents, Position Pos,
                             llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS,
                             const SymbolIndex *Index) {
diff --git a/clang-tools-extra/clangd/unittests/ClangdTests.cpp b/clang-tools-extra/clangd/unittests/ClangdTests.cpp
--- a/clang-tools-extra/clangd/unittests/ClangdTests.cpp
+++ b/clang-tools-extra/clangd/unittests/ClangdTests.cpp
@@ -552,15 +552,13 @@
   EXPECT_ERROR(runFindDocumentHighlights(Server, FooCpp, Position()));
   EXPECT_ERROR(runRename(Server, FooCpp, Position(), "new_name",
                          clangd::RenameOptions()));
+  EXPECT_ERROR(runSignatureHelp(Server, FooCpp, Position()));
   // Identifier-based fallback completion.
   EXPECT_THAT(cantFail(runCodeComplete(Server, FooCpp, Position(),
                                        clangd::CodeCompleteOptions()))
                   .Completions,
               ElementsAre(Field(&CodeCompletion::Name, "int"),
                           Field(&CodeCompletion::Name, "main")));
-  auto SigHelp = runSignatureHelp(Server, FooCpp, Position());
-  ASSERT_TRUE(bool(SigHelp)) << "signatureHelp returned an error";
-  EXPECT_THAT(SigHelp->signatures, IsEmpty());
 }
 
 class ClangdThreadingTest : public ClangdVFSTest {};
diff --git a/clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp b/clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp
--- a/clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp
+++ b/clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp
@@ -1049,8 +1049,12 @@
   auto Preamble =
       buildPreamble(testPath(TU.Filename), *CI, /*OldPreamble=*/nullptr, Inputs,
                     /*InMemory=*/true, /*Callback=*/nullptr);
-  return signatureHelp(testPath(TU.Filename), Inputs.CompileCommand,
-                       Preamble.get(), Text, Point, Inputs.FS, Index.get());
+  if (!Preamble) {
+    ADD_FAILURE() << "Couldn't build Preamble";
+    return {};
+  }
+  return signatureHelp(testPath(TU.Filename), Inputs.CompileCommand, *Preamble,
+                       Text, Point, Inputs.FS, Index.get());
 }
 
 SignatureHelp signatures(llvm::StringRef Text,