diff --git a/src/challenge/mod.rs b/src/challenge/mod.rs
index d0b76a5..48fa063 100644
--- a/src/challenge/mod.rs
+++ b/src/challenge/mod.rs
@@ -41,7 +41,7 @@ impl ChallengeDesc {
             hints: hints.iter().map(|a| a.to_string()).collect(),
             solution: solution.to_string(),
             description: description.to_string(),
-            addr: SocketAddr::new(base_addr.ip(), base_addr.port() + id as u16),
+            addr: SocketAddr::new(base_addr.ip(), base_addr.port() + id as u16 - 1),
         }
     }
     /// Returns a [`SocketAddr`] for the challenge.