diff --git a/iroh-relay/src/client.rs b/iroh-relay/src/client.rs
index 09906576b1..b00181fd86 100644
--- a/iroh-relay/src/client.rs
+++ b/iroh-relay/src/client.rs
@@ -227,7 +227,7 @@ impl ClientBuilder {
             #[cfg(any(test, feature = "test-utils"))]
             insecure_skip_cert_verify: false,
             proxy_url: None,
-            key_cache_capacity: 0,
+            key_cache_capacity: 128,
         }
     }
 
diff --git a/iroh-relay/src/key_cache.rs b/iroh-relay/src/key_cache.rs
index 2c6563a9cc..6766a2f446 100644
--- a/iroh-relay/src/key_cache.rs
+++ b/iroh-relay/src/key_cache.rs
@@ -9,10 +9,15 @@ type SignatureError = <PublicKey as TryFrom<&'static [u8]>>::Error;
 type PublicKeyBytes = [u8; PublicKey::LENGTH];
 
 /// A cache for public keys.
-#[derive(Debug, Clone, Default)]
+///
+/// This is used solely to make parsing public keys from byte slices more
+/// efficient for the very common case where a large number of identical keys
+/// are being parsed, like in the relay server.
+///
+/// The cache stores only successful parse results.
+#[derive(Debug, Clone)]
 pub enum KeyCache {
     /// The key cache is disabled.
-    #[default]
     Disabled,
     /// The key cache is enabled with a fixed capacity. It is shared between
     /// multiple threads.
@@ -43,6 +48,8 @@ impl KeyCache {
             return PublicKey::try_from(slice);
         };
         let Ok(bytes) = PublicKeyBytes::try_from(slice) else {
+            // if the size is wrong, use PublicKey::try_from to fail with a
+            // SignatureError.
             PublicKey::try_from(slice)?;
             unreachable!();
         };
diff --git a/iroh-relay/src/server/http_server.rs b/iroh-relay/src/server/http_server.rs
index 535b46e93a..c9d6865b5d 100644
--- a/iroh-relay/src/server/http_server.rs
+++ b/iroh-relay/src/server/http_server.rs
@@ -175,7 +175,7 @@ impl ServerBuilder {
             handlers: Default::default(),
             headers: HeaderMap::new(),
             client_rx_ratelimit: None,
-            key_cache_capacity: 0,
+            key_cache_capacity: 1024 * 1024,
         }
     }