diff --git a/nostr-sdk/CHANGELOG.md b/nostr-sdk/CHANGELOG.md
index 822d77b4f..28ec27040 100644
--- a/nostr-sdk/CHANGELOG.md
+++ b/nostr-sdk/CHANGELOG.md
@@ -29,6 +29,10 @@
 
 ## Unreleased
 
+### Added
+
+- local-relay: Add `LocalRelayBuilderNip42::relay_url` (https://github.com/nostrdevkit/nostr/pull/1476) to make it possible to configure a custom `relay_url` for the nip42 challenge validation
+
 ### Deprecated
 
 - Deprecate `LocalRelayBuilder::max_query_results` and `LocalRelayBuilder::default_filter_limit` (https://github.com/nostrdevkit/nostr/pull/1461)
diff --git a/nostr-sdk/src/local_relay/builder.rs b/nostr-sdk/src/local_relay/builder.rs
index 8c9916d81..8356ccc7f 100644
--- a/nostr-sdk/src/local_relay/builder.rs
+++ b/nostr-sdk/src/local_relay/builder.rs
@@ -230,6 +230,10 @@ pub struct LocalRelayBuilderNip42 {
     pub mode: LocalRelayBuilderNip42Mode,
     // /// Allowed public keys
     // pub allowed: HashSet<PublicKey>,
+    /// Relay URL expected in NIP-42 authentication events.
+    ///
+    /// If not set, the local relay's listening URL is used.
+    pub relay_url: Option<RelayUrl>,
 }
 
 impl LocalRelayBuilderNip42 {
@@ -238,6 +242,7 @@ impl LocalRelayBuilderNip42 {
     pub fn write() -> Self {
         Self {
             mode: LocalRelayBuilderNip42Mode::Write,
+            relay_url: None,
         }
     }
 
@@ -246,6 +251,7 @@ impl LocalRelayBuilderNip42 {
     pub fn read() -> Self {
         Self {
             mode: LocalRelayBuilderNip42Mode::Read,
+            relay_url: None,
         }
     }
 
@@ -254,8 +260,16 @@ impl LocalRelayBuilderNip42 {
     pub fn read_and_write() -> Self {
         Self {
             mode: LocalRelayBuilderNip42Mode::Both,
+            relay_url: None,
         }
     }
+
+    /// Set the relay URL expected in NIP-42 authentication events.
+    #[inline]
+    pub fn relay_url(mut self, url: RelayUrl) -> Self {
+        self.relay_url = Some(url);
+        self
+    }
 }
 
 #[allow(missing_docs)]
diff --git a/nostr-sdk/src/local_relay/local/inner.rs b/nostr-sdk/src/local_relay/local/inner.rs
index a49036972..397935e31 100644
--- a/nostr-sdk/src/local_relay/local/inner.rs
+++ b/nostr-sdk/src/local_relay/local/inner.rs
@@ -917,7 +917,12 @@ impl InnerLocalRelay {
                     .await;
                 }
 
-                match session.nip42.check_challenge(&event, &self.url().await) {
+                let relay_url: RelayUrl =
+                    match self.nip42.as_ref().and_then(|opts| opts.relay_url.as_ref()) {
+                        Some(url) => url.clone(),
+                        None => self.url().await,
+                    };
+                match session.nip42.check_challenge(&event, &relay_url) {
                     Ok(()) => {
                         send_msg(
                             ws_tx,
diff --git a/nostr-sdk/src/relay/api/send_event.rs b/nostr-sdk/src/relay/api/send_event.rs
index 416496f5f..030da55f5 100644
--- a/nostr-sdk/src/relay/api/send_event.rs
+++ b/nostr-sdk/src/relay/api/send_event.rs
@@ -342,6 +342,7 @@ mod tests {
         // Mock relay
         let opts = LocalRelayBuilderNip42 {
             mode: LocalRelayBuilderNip42Mode::Write,
+            relay_url: None,
         };
         let mock = LocalRelay::builder().nip42(opts).build();
         mock.run().await.unwrap();
@@ -370,6 +371,7 @@ mod tests {
         // Mock relay
         let opts = LocalRelayBuilderNip42 {
             mode: LocalRelayBuilderNip42Mode::Write,
+            relay_url: None,
         };
         let mock = LocalRelay::builder().nip42(opts).build();
         mock.run().await.unwrap();