diff --git a/changelog.d/7167.doc b/changelog.d/7167.doc
new file mode 100644
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@@ -0,0 +1 @@
+Improve README.md by being explicit about public IP recommendation for TURN relaying.
diff --git a/docs/turn-howto.md b/docs/turn-howto.md
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--- a/docs/turn-howto.md
+++ b/docs/turn-howto.md
@@ -11,6 +11,13 @@ TURN server.
 
 The following sections describe how to install [coturn](<https://github.com/coturn/coturn>) (which implements the TURN REST API) and integrate it with synapse.
 
+## Requirements
+
+For TURN relaying with `coturn` to work, it must be hosted on a server/endpoint with a public IP.
+
+Hosting TURN behind a NAT (even with appropriate port forwarding) is known to cause issues
+and to often not work.
+
 ## `coturn` Setup
 
 ### Initial installation