diff --git a/swh/journal/tests/test_kafka_writer.py b/swh/journal/tests/test_kafka_writer.py
--- a/swh/journal/tests/test_kafka_writer.py
+++ b/swh/journal/tests/test_kafka_writer.py
@@ -74,7 +74,7 @@
     kafka_prefix += '.swh.journal.objects'
 
     config = {
-        'brokers': 'localhost:%d' % kafka_server[1],
+        'brokers': ['localhost:%d' % kafka_server[1]],
         'client_id': 'kafka_writer',
         'prefix': kafka_prefix,
     }
@@ -102,7 +102,7 @@
     kafka_prefix += '.swh.journal.objects'
 
     config = {
-        'brokers': 'localhost:%d' % kafka_server[1],
+        'brokers': ['localhost:%d' % kafka_server[1]],
         'client_id': 'kafka_writer',
         'prefix': kafka_prefix,
     }
diff --git a/swh/journal/writer/kafka.py b/swh/journal/writer/kafka.py
--- a/swh/journal/writer/kafka.py
+++ b/swh/journal/writer/kafka.py
@@ -22,8 +22,11 @@
     def __init__(self, brokers, prefix, client_id):
         self._prefix = prefix
 
+        if isinstance(brokers, str):
+            brokers = [brokers]
+
         self.producer = Producer({
-            'bootstrap.servers': brokers,
+            'bootstrap.servers': ','.join(brokers),
             'client.id': client_id,
             'enable.idempotence': 'true',
         })
@@ -35,11 +38,12 @@
             value=value_to_kafka(value),
         )
 
-    def flush(self):
-        self.producer.flush()
         # Need to service the callbacks regularly by calling poll
         self.producer.poll(0)
 
+    def flush(self):
+        self.producer.flush()
+
     def _get_key(self, object_type, object_):
         if object_type in ('revision', 'release', 'directory', 'snapshot'):
             return object_['id']