Index: clang-tools-extra/trunk/clangd/index/Index.h
===================================================================
--- clang-tools-extra/trunk/clangd/index/Index.h
+++ clang-tools-extra/trunk/clangd/index/Index.h
@@ -437,7 +437,9 @@
   std::vector<std::string> Scopes;
   /// \brief The number of top candidates to return. The index may choose to
   /// return more than this, e.g. if it doesn't know which candidates are best.
-  size_t MaxCandidateCount = std::numeric_limits<size_t>::max();
+  // FIXME: Use llvm::Optional; semantically, the absence of MaxCandidateCount
+  // is equivalent to setting this field to default value as below.
+  uint32_t MaxCandidateCount = std::numeric_limits<uint32_t>::max();
   /// If set to true, only symbols for completion support will be considered.
   bool RestrictForCodeCompletion = false;
   /// Contextually relevant files (e.g. the file we're code-completing in).
Index: clang-tools-extra/trunk/clangd/index/Index.cpp
===================================================================
--- clang-tools-extra/trunk/clangd/index/Index.cpp
+++ clang-tools-extra/trunk/clangd/index/Index.cpp
@@ -177,29 +177,25 @@
 
 bool fromJSON(const llvm::json::Value &Parameters, FuzzyFindRequest &Request) {
   json::ObjectMapper O(Parameters);
-  llvm::Optional<int64_t> MaxCandidateCount;
+  int64_t MaxCandidateCount;
   bool OK =
       O && O.map("Query", Request.Query) && O.map("Scopes", Request.Scopes) &&
+      O.map("MaxCandidateCount", MaxCandidateCount) &&
       O.map("RestrictForCodeCompletion", Request.RestrictForCodeCompletion) &&
-      O.map("ProximityPaths", Request.ProximityPaths) &&
-      O.map("MaxCandidateCount", MaxCandidateCount);
-  if (MaxCandidateCount)
-    Request.MaxCandidateCount = MaxCandidateCount.getValue();
+      O.map("ProximityPaths", Request.ProximityPaths);
+  if (OK && MaxCandidateCount <= std::numeric_limits<uint32_t>::max())
+    Request.MaxCandidateCount = MaxCandidateCount;
   return OK;
 }
 
 llvm::json::Value toJSON(const FuzzyFindRequest &Request) {
-  auto Result = json::Object{
+  return json::Object{
       {"Query", Request.Query},
       {"Scopes", json::Array{Request.Scopes}},
+      {"MaxCandidateCount", Request.MaxCandidateCount},
       {"RestrictForCodeCompletion", Request.RestrictForCodeCompletion},
       {"ProximityPaths", json::Array{Request.ProximityPaths}},
   };
-  // A huge limit means no limit, leave it out.
-  if (Request.MaxCandidateCount <= std::numeric_limits<int64_t>::max())
-    Result["MaxCandidateCount"] =
-        static_cast<int64_t>(Request.MaxCandidateCount);
-  return std::move(Result);
 }
 
 bool SwapIndex::fuzzyFind(const FuzzyFindRequest &R,