diff --git a/neqo-transport/src/connection/state.rs b/neqo-transport/src/connection/state.rs
index 9789151d3f..cc2f6e30d2 100644
--- a/neqo-transport/src/connection/state.rs
+++ b/neqo-transport/src/connection/state.rs
@@ -209,7 +209,10 @@ pub enum StateSignaling {
 impl StateSignaling {
     pub fn handshake_done(&mut self) {
         if !matches!(self, Self::Idle) {
-            debug_assert!(false, "StateSignaling must be in Idle state.");
+            debug_assert!(
+                false,
+                "StateSignaling must be in Idle state but is in {self:?} state.",
+            );
             return;
         }
         *self = Self::HandshakeDone;