Refer to std string and stream with their fully qualified names.
diff --git a/src/vk_mem_alloc.h b/src/vk_mem_alloc.h
index d0277d8..6687871 100644
--- a/src/vk_mem_alloc.h
+++ b/src/vk_mem_alloc.h
@@ -15602,9 +15602,9 @@
         // There is room for optimization since sstream is quite slow.

         // Is there a better way to convert std::this_thread::get_id() to uint32_t?

         std::thread::id thread_id = std::this_thread::get_id();

-        stringstream thread_id_to_string_converter;

+        std::stringstream thread_id_to_string_converter;

         thread_id_to_string_converter << thread_id;

-        string thread_id_as_string = thread_id_to_string_converter.str();

+        std::string thread_id_as_string = thread_id_to_string_converter.str();

         outParams.threadId = static_cast<uint32_t>(std::stoi(thread_id_as_string.c_str()));

     #endif