diff --git a/tests/kafkatest/tests/core/downgrade_test.py b/tests/kafkatest/tests/core/downgrade_test.py
index bd306d83c204..2ec453a90243 100644
--- a/tests/kafkatest/tests/core/downgrade_test.py
+++ b/tests/kafkatest/tests/core/downgrade_test.py
@@ -41,7 +41,7 @@ def upgrade_from(self, kafka_version):
             node.config[config_property.INTER_BROKER_PROTOCOL_VERSION] = str(kafka_version)
             node.config[config_property.MESSAGE_FORMAT_VERSION] = str(kafka_version)
             self.kafka.start_node(node)
-            self.kafka.await_no_under_replicated_partitions(timeout_sec=60)
+            self.wait_until_rejoin()
 
     def downgrade_to(self, kafka_version):
         for node in self.kafka.nodes:
@@ -50,7 +50,7 @@ def downgrade_to(self, kafka_version):
             del node.config[config_property.INTER_BROKER_PROTOCOL_VERSION]
             del node.config[config_property.MESSAGE_FORMAT_VERSION]
             self.kafka.start_node(node)
-            self.kafka.await_no_under_replicated_partitions(timeout_sec=60)
+            self.wait_until_rejoin()
 
     def setup_services(self, kafka_version, compression_types, security_protocol, static_membership):
         self.create_zookeeper_if_necessary()
@@ -73,6 +73,11 @@ def setup_services(self, kafka_version, compression_types, security_protocol, st
 
         self.consumer.start()
 
+    def wait_until_rejoin(self):
+        for partition in range(0, self.PARTITIONS):
+            wait_until(lambda: len(self.kafka.isr_idx_list(self.topic, partition)) == self.REPLICATION_FACTOR, 
+                    timeout_sec=60, backoff_sec=1, err_msg="Replicas did not rejoin the ISR in a reasonable amount of time")
+
     @cluster(num_nodes=7)
     @parametrize(version=str(LATEST_2_8), compression_types=["snappy"])
     @parametrize(version=str(LATEST_2_8), compression_types=["zstd"], security_protocol="SASL_SSL")
diff --git a/tests/kafkatest/tests/core/upgrade_test.py b/tests/kafkatest/tests/core/upgrade_test.py
index 339424c64b83..7fd4ab84a96b 100644
--- a/tests/kafkatest/tests/core/upgrade_test.py
+++ b/tests/kafkatest/tests/core/upgrade_test.py
@@ -42,6 +42,11 @@ def setUp(self):
         self.num_producers = 1
         self.num_consumers = 1
 
+    def wait_until_rejoin(self):
+        for partition in range(0, self.partitions):
+            wait_until(lambda: len(self.kafka.isr_idx_list(self.topic, partition)) == self.replication_factor, timeout_sec=60,
+                    backoff_sec=1, err_msg="Replicas did not rejoin the ISR in a reasonable amount of time")
+
     def perform_upgrade(self, from_kafka_version, to_message_format_version=None):
         self.logger.info("Upgrade ZooKeeper from %s to %s" % (str(self.zk.nodes[0].version), str(DEV_BRANCH)))
         self.zk.set_version(DEV_BRANCH)
@@ -69,7 +74,7 @@ def perform_upgrade(self, from_kafka_version, to_message_format_version=None):
             node.config[config_property.INTER_BROKER_PROTOCOL_VERSION] = from_kafka_version
             node.config[config_property.MESSAGE_FORMAT_VERSION] = from_kafka_version
             self.kafka.start_node(node)
-            self.kafka.await_no_under_replicated_partitions(timeout_sec=60)
+            self.wait_until_rejoin()
 
         self.logger.info("Third pass bounce - remove inter.broker.protocol.version config")
         for node in self.kafka.nodes:
@@ -83,7 +88,7 @@ def perform_upgrade(self, from_kafka_version, to_message_format_version=None):
                     node.config[config_property.INTER_BROKER_PROTOCOL_VERSION] = str(V_2_8_0)
                 node.config[config_property.MESSAGE_FORMAT_VERSION] = to_message_format_version
             self.kafka.start_node(node)
-            self.kafka.await_no_under_replicated_partitions(timeout_sec=60)
+            self.wait_until_rejoin()
 
     @cluster(num_nodes=6)
     @parametrize(from_kafka_version=str(LATEST_2_8), to_message_format_version=None, compression_types=["none"])