diff --git a/changelog.d/4458.misc b/changelog.d/4458.misc
new file mode 100644
index 000000000..8b3bc94a3
--- /dev/null
+++ b/changelog.d/4458.misc
@@ -0,0 +1 @@
+Clarify documentation for the `public_baseurl` config param
diff --git a/synapse/config/server.py b/synapse/config/server.py
index fb5779109..bc97b44a5 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -256,7 +256,11 @@ class ServerConfig(Config):
         #
         # web_client_location: "/path/to/web/root"
 
-        # The public-facing base URL for the client API (not including _matrix/...)
+        # The public-facing base URL that clients use to access this HS
+        # (not including _matrix/...). This is the same URL a user would
+        # enter into the 'custom HS URL' field on their client. If you
+        # use synapse with a reverse proxy, this should be the URL to reach
+        # synapse via the proxy.
         # public_baseurl: https://example.com:8448/
 
         # Set the soft limit on the number of file descriptors synapse can use