diff --git a/interop.py b/interop.py
index 0a7126d7..8f2769b8 100644
--- a/interop.py
+++ b/interop.py
@@ -240,7 +240,7 @@ def get_letters(result):
                         results.append(colored(measurement.abbreviation(), "grey"))
                     elif res.result == TestResult.FAILED:
                         results.append(colored(measurement.abbreviation(), "red"))
-                row[server] += "\n".join(results)
+                row[server] = "\n".join(results)
             t.field_names = [""] + [column for column, _ in columns.items()]
             for client, results in rows.items():
                 row = [client]