diff --git a/prototypes/ptth_quic_client_gui/src/main.rs b/prototypes/ptth_quic_client_gui/src/main.rs
index ad1c3f6..077f60a 100644
--- a/prototypes/ptth_quic_client_gui/src/main.rs
+++ b/prototypes/ptth_quic_client_gui/src/main.rs
@@ -224,7 +224,7 @@ fn main () -> anyhow::Result <()> {
 	let connection_p2_p3 = rt.block_on (async move {
 		let server_cert = match opt.cert_url.as_ref () {
 			Some (url) => reqwest::get (url).await?.bytes ().await?,
-			None => tokio::fs::read ("ptth_quic_output/quic_server.crt").await?.into (),
+			None => tokio::fs::read ("ptth_quic_output/quic_server.crt").await.context ("can't read quic_server.crt from disk")?.into (),
 		};
 		
 		let endpoint = make_client_endpoint ("0.0.0.0:0".parse ()?, &[&server_cert])?;