diff --git a/cmd/server/main.go b/cmd/server/main.go
index 87334e8..3ddca3f 100644
--- a/cmd/server/main.go
+++ b/cmd/server/main.go
@@ -44,6 +44,12 @@ func main() {
 		DisableStartupMessage: true,
 		ReadTimeout:           10 * time.Second,
 		WriteTimeout:          10 * time.Second,
+		// fasthttp defaults to a 4 KB read buffer per connection;
+		// any request whose header line exceeds that returns a flat
+		// HTTP 431 before any handler runs. 16 KB matches the
+		// cluster's nginx-ingress large_client_header buffer and
+		// accommodates chunked NextAuth cookies + large bearer tokens.
+		ReadBufferSize: 16384,
 	})
 	app.Use(recover.New())
 	app.Use(logger.New(logger.Config{