diff --git a/core/src/main/scala/kafka/coordinator/group/GroupMetadataManager.scala b/core/src/main/scala/kafka/coordinator/group/GroupMetadataManager.scala
index 8cf99fcc438..dba8b4e1810 100644
--- a/core/src/main/scala/kafka/coordinator/group/GroupMetadataManager.scala
+++ b/core/src/main/scala/kafka/coordinator/group/GroupMetadataManager.scala
@@ -40,7 +40,7 @@ import org.apache.kafka.common.protocol.Errors
 import org.apache.kafka.common.protocol.types.Type._
 import org.apache.kafka.common.protocol.types._
 import org.apache.kafka.common.record._
-import org.apache.kafka.common.requests.{IsolationLevel, OffsetFetchResponse}
+import org.apache.kafka.common.requests.{IsolationLevel, OffsetCommitRequest, OffsetFetchResponse}
 import org.apache.kafka.common.requests.ProduceResponse.PartitionResponse
 import org.apache.kafka.common.utils.{Time, Utils}
 
@@ -1129,7 +1129,7 @@ object GroupMetadataManager {
       value.set(OFFSET_VALUE_METADATA_FIELD_V1, offsetAndMetadata.metadata)
       value.set(OFFSET_VALUE_COMMIT_TIMESTAMP_FIELD_V1, offsetAndMetadata.commitTimestamp)
       // version 1 has a non empty expireTimestamp field
-      value.set(OFFSET_VALUE_EXPIRE_TIMESTAMP_FIELD_V1, offsetAndMetadata.expireTimestamp.get)
+      value.set(OFFSET_VALUE_EXPIRE_TIMESTAMP_FIELD_V1, offsetAndMetadata.expireTimestamp.getOrElse(OffsetCommitRequest.DEFAULT_TIMESTAMP))
     }
 
     val byteBuffer = ByteBuffer.allocate(2 /* version */ + value.sizeOf)
diff --git a/core/src/main/scala/kafka/server/KafkaApis.scala b/core/src/main/scala/kafka/server/KafkaApis.scala
index afbe5b88204..10119c8d632 100644
--- a/core/src/main/scala/kafka/server/KafkaApis.scala
+++ b/core/src/main/scala/kafka/server/KafkaApis.scala
@@ -332,11 +332,10 @@ class KafkaApis(val requestChannel: RequestChannel,
       } else {
         // for version 1 and beyond store offsets in offset manager
 
-        // commit timestamp is always set to now.
         // "default" expiration timestamp is now + retention (and retention may be overridden if v2)
         // expire timestamp is computed differently for v1 and v2.
         //   - If v1 and no explicit commit timestamp is provided we treat it the same as v5.
-        //   - If v1 and explicit commit timestamp is provided we calculate retention from that explicit commit timestamp
+        //   - If v1 and explicit retention time is provided we calculate expiration timestamp based on that
         //   - If v2/v3/v4 (no explicit commit timestamp) we treat it the same as v5.
         //   - For v5 and beyond there is no per partition expiration timestamp, so this field is no longer in effect
         val currentTimestamp = time.milliseconds