diff --git a/docs/PROXY_WASM.md b/docs/PROXY_WASM.md
index 0b98595e1..6d92f0da8 100644
--- a/docs/PROXY_WASM.md
+++ b/docs/PROXY_WASM.md
@@ -749,6 +749,11 @@ payloads.
    eviction mechanism when the allocated memory slab is full:
     - `proxy_enqueue_shared_queue`
 
+5. In ngx_wasm_module, metric names are prefixed with `pw.filter_name.`, where
+   `filter_name` represents the name assigned to the filter in which the metric
+   is defined.
+   In Envoy, however, metric names are prefixed with `wasmcustom.`.
+
 Future ngx_wasm_module and WasmX work will be aimed at lifting these
 limitations when possible and increasing overall surface support for the
 Proxy-Wasm SDK.