diff --git a/src/confluent_kafka/kafkatest/verifiable_client.py b/src/confluent_kafka/kafkatest/verifiable_client.py
index 56d4383e3..c91b6ff13 100644
--- a/src/confluent_kafka/kafkatest/verifiable_client.py
+++ b/src/confluent_kafka/kafkatest/verifiable_client.py
@@ -108,7 +108,7 @@ def read_config_file(path):
 
                 fi = line.find('=')
                 if fi < 1:
-                    raise Exception('%s: invalid line, no key=value pair: %s' % (path, line))
+                    raise Exception(f'{path}: invalid line, no key=value pair: {line}')
 
                 k = line[:fi]
                 v = line[fi+1:]