diff --git a/include/wrenpp/detail/guess_class_name.hpp b/include/wrenpp/detail/guess_class_name.hpp
index ea47067..5b3e0c1 100644
--- a/include/wrenpp/detail/guess_class_name.hpp
+++ b/include/wrenpp/detail/guess_class_name.hpp
@@ -61,7 +61,7 @@ namespace wren {
 			constexpr auto from = last_whatever + (last_whatever == fname_len ? 0 : 1);
 			constexpr auto len = detail::find_token_end(fname + from, fname_len - from);
 
-			constexpr dhandy::bt::string<len> retval{fname + from, 0};
+			constexpr dhandy::bt::string<len+1> retval{fname + from, 0};
 			return retval;
 	//#elif defined(_MSC_VER)
 			//void __cdecl guess_class_name<class MyTest>(void)