diff --git a/src/main/java/org/embulk/input/marketo/delegate/ProgramMembersBulkExtractInputPlugin.java b/src/main/java/org/embulk/input/marketo/delegate/ProgramMembersBulkExtractInputPlugin.java
index bdac277..c377f6e 100644
--- a/src/main/java/org/embulk/input/marketo/delegate/ProgramMembersBulkExtractInputPlugin.java
+++ b/src/main/java/org/embulk/input/marketo/delegate/ProgramMembersBulkExtractInputPlugin.java
@@ -55,6 +55,7 @@
 public class ProgramMembersBulkExtractInputPlugin extends MarketoBaseInputPluginDelegate<ProgramMembersBulkExtractInputPlugin.PluginTask>
 {
     private final Logger logger = LoggerFactory.getLogger(getClass());
+    private final Object pageBuilderLock = new Object();
 
     public interface PluginTask extends MarketoBaseInputPluginDelegate.PluginTask, CsvTokenizer.PluginTask
     {
@@ -214,7 +215,9 @@ private Future<?> createFutureTask(PluginTask task, RecordImporter recordImporte
                 while (csvRecords.hasNext()) {
                     Map<String, String> csvRecord = csvRecords.next();
                     ObjectNode objectNode = MarketoUtils.OBJECT_MAPPER.valueToTree(csvRecord);
-                    recordImporter.importRecord(new AllStringJacksonServiceRecord(objectNode), pageBuilder);
+                    synchronized (pageBuilderLock) {
+                        recordImporter.importRecord(new AllStringJacksonServiceRecord(objectNode), pageBuilder);
+                    }
                     imported = imported + 1;
                 }