diff --git a/src/language_server_api.cc b/src/language_server_api.cc
index 9c1acf4a..c4fe1a8f 100644
--- a/src/language_server_api.cc
+++ b/src/language_server_api.cc
@@ -5,6 +5,13 @@
 #include <doctest/doctest.h>
 #include <loguru.hpp>
 
+void Reflect(Reader& visitor, std::variant<std::monostate, int>& version) {
+  if (visitor.IsNull())
+    version = std::monostate();
+  else
+    version = visitor.GetInt();
+}
+
 void Reflect(Reader& visitor, lsRequestId& id) {
   if (visitor.IsInt()) {
     int v;
diff --git a/src/language_server_api.h b/src/language_server_api.h
index 120207de..3e6b6ee9 100644
--- a/src/language_server_api.h
+++ b/src/language_server_api.h
@@ -11,8 +11,6 @@
 #include <variant.h>
 
 #include <algorithm>
-#include <iostream>
-#include <sstream>
 #include <unordered_map>
 #include <unordered_set>
 
@@ -254,10 +252,11 @@ struct lsTextDocumentIdentifier {
 };
 MAKE_REFLECT_STRUCT(lsTextDocumentIdentifier, uri);
 
+void Reflect(Reader& visitor, std::variant<std::monostate, int>& version);
 struct lsVersionedTextDocumentIdentifier {
   lsDocumentUri uri;
-  // The version number of this document.
-  optional<int> version;
+  // The version number of this document.  number | null
+  std::variant<std::monostate, int> version;
 
   lsTextDocumentIdentifier AsTextDocumentIdentifier() const;
 };
diff --git a/src/serializer.h b/src/serializer.h
index a1b7fb42..2f1d1359 100644
--- a/src/serializer.h
+++ b/src/serializer.h
@@ -160,6 +160,12 @@ void Reflect(Writer& visitor, bool& value);
 void Reflect(Reader& visitor, std::string& value);
 void Reflect(Writer& visitor, std::string& value);
 
+void Reflect(Reader& visitor, std::monostate&);
+void Reflect(Writer& visitor, std::monostate&);
+
+void Reflect(Reader& visitor, SerializeFormat& value);
+void Reflect(Writer& visitor, SerializeFormat& value);
+
 // std::optional
 template <typename T>
 void Reflect(Reader& visitor, optional<T>& value) {
@@ -272,14 +278,6 @@ void ReflectMember(Reader& visitor, const char* name, T& value) {
   visitor.DoMember(name, [&](Reader& child) { Reflect(child, value); });
 }
 
-// Specializations
-
-void Reflect(Reader& visitor, std::monostate&);
-void Reflect(Writer& visitor, std::monostate&);
-
-void Reflect(Reader& visitor, SerializeFormat& value);
-void Reflect(Writer& visitor, SerializeFormat& value);
-
 // API
 
 std::string Serialize(SerializeFormat format, IndexFile& file);
diff --git a/src/working_files.cc b/src/working_files.cc
index 5b62fd17..086ee58f 100644
--- a/src/working_files.cc
+++ b/src/working_files.cc
@@ -317,8 +317,9 @@ void WorkingFiles::OnChange(const lsTextDocumentDidChangeParams& change) {
     return;
   }
 
-  if (change.textDocument.version)
-    file->version = *change.textDocument.version;
+  // version: number | null
+  if (std::holds_alternative<int>(change.textDocument.version))
+    file->version = std::get<int>(change.textDocument.version);
 
   for (const lsTextDocumentContentChangeEvent& diff : change.contentChanges) {
     // Per the spec replace everything if the rangeLength and range are not set.