diff --git a/lsp-server/src/protocol/detail/document_sync.hpp b/lsp-server/src/protocol/detail/document_sync.hpp
index dfeb601..0929520 100644
--- a/lsp-server/src/protocol/detail/document_sync.hpp
+++ b/lsp-server/src/protocol/detail/document_sync.hpp
@@ -40,7 +40,7 @@ namespace lsp::protocol
 
     struct VersionedTextDocumentIdentifier : TextDocumentIdentifier
     {
-        integer version;
+        std::optional<integer> version;
     };
 
     struct OptionalVersionedTextDocumentIdentifier : TextDocumentIdentifier