diff --git a/src/messages/cquery_member_hierarchy.cc b/src/messages/cquery_member_hierarchy.cc
index df8b0ecd..0ef2e273 100644
--- a/src/messages/cquery_member_hierarchy.cc
+++ b/src/messages/cquery_member_hierarchy.cc
@@ -17,8 +17,9 @@ struct Ipc_CqueryMemberHierarchyExpand
   const static IpcId kIpcId = IpcId::CqueryMemberHierarchyExpand;
   lsRequestId id;
   struct Params {
-    size_t type_id;
-  } params;
+    uint64_t type_id;
+  };
+  Params params;
 };
 MAKE_REFLECT_STRUCT(Ipc_CqueryMemberHierarchyExpand::Params, type_id);
 MAKE_REFLECT_STRUCT(Ipc_CqueryMemberHierarchyExpand, id, params);
@@ -28,7 +29,7 @@ struct Out_CqueryMemberHierarchy
     : public lsOutMessage<Out_CqueryMemberHierarchy> {
   struct Entry {
     std::string name;
-    uint64_t type_id;
+    uint64_t type_id; // FIXME: should be size_t
     lsLocation location;
   };
   lsRequestId id;
@@ -73,7 +74,7 @@ ExpandNode(QueryDatabase* db,
     Out_CqueryMemberHierarchy::Entry entry;
     entry.name = var.def->short_name;
     entry.type_id =
-        var.def->variable_type ? var.def->variable_type->id : size_t(-1);
+        var.def->variable_type ? var.def->variable_type->id : uint64_t(-1);
     if (var.def->definition_spelling) {
       optional<lsLocation> loc =
           GetLsLocation(db, working_files, *var.def->definition_spelling);
@@ -124,7 +125,7 @@ struct CqueryMemberHierarchyExpandHandler
     Out_CqueryMemberHierarchy out;
     out.id = request->id;
     // |ExpandNode| uses -1 to indicate invalid |type_id|.
-    if (request->params.type_id != size_t(-1))
+    if (request->params.type_id != uint64_t(-1))
       out.result =
           ExpandNode(db, working_files, QueryTypeId(request->params.type_id));