diff --git a/qiskit_addon_obp/backpropagation.py b/qiskit_addon_obp/backpropagation.py
index 5c69429..a9d804c 100644
--- a/qiskit_addon_obp/backpropagation.py
+++ b/qiskit_addon_obp/backpropagation.py
@@ -215,7 +215,7 @@ def handle_timeout(signum, frame):
                         )
 
                     LOGGER.debug(
-                        f"Size of the observable after backpropagating the {op_idx}-th gate in "
+                        f"Size of the observable after backpropagating gate id {len(op_nodes)-op_idx-1} in "
                         f"the current layer: {len(observables_tmp[i])}"
                     )