diff --git a/clients/src/main/java/org/apache/kafka/clients/consumer/internals/StreamsGroupHeartbeatRequestManager.java b/clients/src/main/java/org/apache/kafka/clients/consumer/internals/StreamsGroupHeartbeatRequestManager.java
index bd554051f30b4..0f2f327826626 100644
--- a/clients/src/main/java/org/apache/kafka/clients/consumer/internals/StreamsGroupHeartbeatRequestManager.java
+++ b/clients/src/main/java/org/apache/kafka/clients/consumer/internals/StreamsGroupHeartbeatRequestManager.java
@@ -834,8 +834,21 @@ private static Map<StreamsRebalanceData.HostInfo, StreamsRebalanceData.EndpointP
             List<TopicPartition> activeTopicPartitions = getTopicPartitionList(endpoint.activePartitions());
             List<TopicPartition> standbyTopicPartitions = getTopicPartitionList(endpoint.standbyPartitions());
             StreamsGroupHeartbeatResponseData.Endpoint userEndpoint = endpoint.userEndpoint();
-            StreamsRebalanceData.EndpointPartitions endpointPartitions = new StreamsRebalanceData.EndpointPartitions(activeTopicPartitions, standbyTopicPartitions);
-            partitionsByHost.put(new StreamsRebalanceData.HostInfo(userEndpoint.host(), userEndpoint.port()), endpointPartitions);
+            StreamsRebalanceData.HostInfo hostInfo = new StreamsRebalanceData.HostInfo(userEndpoint.host(), userEndpoint.port());
+            
+            partitionsByHost.merge(
+                hostInfo,
+                new StreamsRebalanceData.EndpointPartitions(activeTopicPartitions, standbyTopicPartitions),
+                (existing, newPartitions) -> {
+                    List<TopicPartition> mergedActive = existing.activePartitions();
+                    mergedActive.addAll(newPartitions.activePartitions());
+                    
+                    List<TopicPartition> mergedStandby = existing.standbyPartitions();
+                    mergedStandby.addAll(newPartitions.standbyPartitions());
+                    
+                    return new StreamsRebalanceData.EndpointPartitions(mergedActive, mergedStandby);
+                }
+            );
         });
         return partitionsByHost;
     }
diff --git a/streams/integration-tests/src/test/java/org/apache/kafka/streams/integration/IQv2EndpointToPartitionsIntegrationTest.java b/streams/integration-tests/src/test/java/org/apache/kafka/streams/integration/IQv2EndpointToPartitionsIntegrationTest.java
index 5b3b789ab10de..fb9304053dd61 100644
--- a/streams/integration-tests/src/test/java/org/apache/kafka/streams/integration/IQv2EndpointToPartitionsIntegrationTest.java
+++ b/streams/integration-tests/src/test/java/org/apache/kafka/streams/integration/IQv2EndpointToPartitionsIntegrationTest.java
@@ -110,6 +110,7 @@ public void shouldGetCorrectHostPartitionInformation(final String groupProtocolC
             streamOneProperties.put(StreamsConfig.STATE_DIR_CONFIG, TestUtils.tempDirectory(appId).getPath() + "-ks1");
             streamOneProperties.put(StreamsConfig.CLIENT_ID_CONFIG, appId + "-ks1");
             streamOneProperties.put(StreamsConfig.APPLICATION_SERVER_CONFIG, "localhost:2020");
+            streamOneProperties.put(StreamsConfig.NUM_STREAM_THREADS_CONFIG, 3);
             streamOneProperties.put(StreamsConfig.GROUP_PROTOCOL_CONFIG, groupProtocolConfig);
             if (usingStandbyReplicas) {
                 streamOneProperties.put(StreamsConfig.NUM_STANDBY_REPLICAS_CONFIG, numStandbyReplicas);