diff --git a/kafka/source.go b/kafka/source.go
index e02769c..e7269ee 100644
--- a/kafka/source.go
+++ b/kafka/source.go
@@ -25,6 +25,12 @@ type SourceConfig struct {
 	BufferSize int
 }
 
+type marker struct {
+	Topic     string
+	Partition int32
+	Offset    int64
+}
+
 // NewSourceConfig creates a new Kafka source configuration.
 func NewSourceConfig() *SourceConfig {
 	c := &SourceConfig{
@@ -132,11 +138,9 @@ func (s *Source) Consume() (*streams.Message, error) {
 
 // Commit marks the consumed records as processed.
 func (s *Source) Commit(v interface{}) error {
-	state := v.(map[string]map[int32]int64)
-	for topic, partitions := range state {
-		for partition, offset := range partitions {
-			s.consumer.MarkPartitionOffset(topic, partition, offset, "")
-		}
+	state := v.([]marker)
+	for _, m := range state {
+		s.consumer.MarkPartitionOffset(m.Topic, m.Partition, m.Offset, "")
 	}
 
 	if err := s.consumer.CommitOffsets(); err != nil {
@@ -151,16 +155,21 @@ func (s *Source) Close() error {
 	return s.consumer.Close()
 }
 
-func (s *Source) markState(msg *sarama.ConsumerMessage) map[string]map[int32]int64 {
+func (s *Source) markState(msg *sarama.ConsumerMessage) []marker {
 	partitions, ok := s.state[msg.Topic]
 	if !ok {
 		partitions = make(map[int32]int64)
 		s.state[msg.Topic] = partitions
 	}
 
-	partitions[msg.Partition] = msg.Offset
+	var markers []marker
+	for topic, partitions := range s.state {
+		for partition, offset := range partitions {
+			markers = append(markers, marker{Topic: topic, Partition: partition, Offset: offset})
+		}
+	}
 
-	return s.state
+	return markers
 }
 
 func (s *Source) readErrors() {