diff --git a/bindings/matrix-sdk-ffi/src/sliding_sync.rs b/bindings/matrix-sdk-ffi/src/sliding_sync.rs
index bc25e654b..c7030acc5 100644
--- a/bindings/matrix-sdk-ffi/src/sliding_sync.rs
+++ b/bindings/matrix-sdk-ffi/src/sliding_sync.rs
@@ -865,12 +865,7 @@ impl Client {
     ///
     /// Note: the identifier must be less than 16 chars long.
     pub fn sliding_sync(&self, id: String) -> Result<Arc<SlidingSyncBuilder>, ClientError> {
-        let mut inner = self.inner.sliding_sync(id)?;
-
-        if let Some(sliding_sync_proxy) = self.inner.sliding_sync_proxy() {
-            inner = inner.sliding_sync_proxy(sliding_sync_proxy);
-        }
-
+        let inner = self.inner.sliding_sync(id)?;
         Ok(Arc::new(SlidingSyncBuilder { inner, client: self.clone() }))
     }
 }
diff --git a/crates/matrix-sdk-ui/src/room_list/mod.rs b/crates/matrix-sdk-ui/src/room_list/mod.rs
index fa1d2329f..5a22081d2 100644
--- a/crates/matrix-sdk-ui/src/room_list/mod.rs
+++ b/crates/matrix-sdk-ui/src/room_list/mod.rs
@@ -96,14 +96,9 @@ impl RoomList {
     /// A [`matrix_sdk::SlidingSync`] client will be created, with a cached list
     /// already pre-configured.
     pub async fn new(client: Client) -> Result<Self, Error> {
-        let mut sliding_sync_builder =
-            client.sliding_sync("room-list").map_err(Error::SlidingSync)?;
-
-        if let Some(sliding_sync_proxy_url) = client.sliding_sync_proxy() {
-            sliding_sync_builder = sliding_sync_builder.sliding_sync_proxy(sliding_sync_proxy_url);
-        }
-
-        let sliding_sync = sliding_sync_builder
+        let sliding_sync = client
+            .sliding_sync("room-list")
+            .map_err(Error::SlidingSync)?
             // Enable the account data extension.
             .with_account_data_extension(
                 assign! { AccountDataConfig::default(), { enabled: Some(true) }},
diff --git a/crates/matrix-sdk/src/sliding_sync/builder.rs b/crates/matrix-sdk/src/sliding_sync/builder.rs
index 3d9b07076..d135fcd67 100644
--- a/crates/matrix-sdk/src/sliding_sync/builder.rs
+++ b/crates/matrix-sdk/src/sliding_sync/builder.rs
@@ -262,6 +262,10 @@ impl SlidingSyncBuilder {
         let rooms = AsyncRwLock::new(self.rooms);
         let lists = AsyncRwLock::new(lists);
 
+        // Use the configured sliding sync proxy, or if not set, try to use the one
+        // auto-discovered by the client, if any.
+        let sliding_sync_proxy = self.sliding_sync_proxy.or_else(|| client.sliding_sync_proxy());
+
         // Always enable to-device events and the e2ee-extension on the initial request,
         // no matter what the caller wants.
         let mut extensions = self.extensions.unwrap_or_default();
@@ -270,7 +274,7 @@ impl SlidingSyncBuilder {
 
         Ok(SlidingSync::new(SlidingSyncInner {
             _id: Some(self.id),
-            sliding_sync_proxy: self.sliding_sync_proxy,
+            sliding_sync_proxy,
             client,
             storage_key: self.storage_key,
 
diff --git a/crates/matrix-sdk/src/sliding_sync/mod.rs b/crates/matrix-sdk/src/sliding_sync/mod.rs
index fc6dc0ee1..1f3d6239a 100644
--- a/crates/matrix-sdk/src/sliding_sync/mod.rs
+++ b/crates/matrix-sdk/src/sliding_sync/mod.rs
@@ -1188,4 +1188,46 @@ mod tests {
 
         Ok(())
     }
+
+    #[tokio::test]
+    async fn test_sliding_sync_proxy_url() -> Result<()> {
+        let server = MockServer::start().await;
+        let client = logged_in_client(Some(server.uri())).await;
+
+        {
+            // A server that doesn't expose a sliding sync proxy gets and transmits none, by
+            // default.
+            let sync = client.sliding_sync("no-proxy")?.build().await?;
+
+            assert!(sync.sliding_sync_proxy().is_none());
+        }
+
+        {
+            // The sliding sync builder can be used to customize a proxy, though.
+            let url = Url::parse("https://bar.matrix/").unwrap();
+            let sync =
+                client.sliding_sync("own-proxy")?.sliding_sync_proxy(url.clone()).build().await?;
+            assert_eq!(sync.sliding_sync_proxy(), Some(url));
+        }
+
+        // Set the client's proxy, that will be inherited by sliding sync.
+        let url = Url::parse("https://foo.matrix/").unwrap();
+        client.set_sliding_sync_proxy(Some(url.clone()));
+
+        {
+            // The sliding sync inherits the client's sliding sync proxy URL.
+            let sync = client.sliding_sync("client-proxy")?.build().await?;
+            assert_eq!(sync.sliding_sync_proxy(), Some(url));
+        }
+
+        {
+            // …unless we override it.
+            let url = Url::parse("https://bar.matrix/").unwrap();
+            let sync =
+                client.sliding_sync("own-proxy")?.sliding_sync_proxy(url.clone()).build().await?;
+            assert_eq!(sync.sliding_sync_proxy(), Some(url));
+        }
+
+        Ok(())
+    }
 }