diff --git a/README.md b/README.md
index d8cdc3f..a2fabe4 100644
--- a/README.md
+++ b/README.md
@@ -8,6 +8,9 @@ It works in both web and Node.js environment (requires Node.js 16.5+).
 
 If you are interested in the main assumptions for Warp ecosystem as well as its key features go visit [our website](https://warp.cc).
 
+⚠️ Do not use "Map" objects in the state of js/ts contracts - since maps by default are not serializable to JSON and won't be properly stored by the caching mechanism. Use "plain" objects instead.
+[More info](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map#objects_vs._maps) - the "Serialization and parsing" row.
+
 - [Development](#development)
   - [Installation](#installation)
     - [Using npm](#using-npm)