diff --git a/server/src/test/java/org/elasticsearch/ingest/SamplingServiceTests.java b/server/src/test/java/org/elasticsearch/ingest/SamplingServiceTests.java
index ad4309740f608..c34f9d33a29d3 100644
--- a/server/src/test/java/org/elasticsearch/ingest/SamplingServiceTests.java
+++ b/server/src/test/java/org/elasticsearch/ingest/SamplingServiceTests.java
@@ -33,6 +33,7 @@
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.xcontent.XContentType;
 
+import java.nio.charset.StandardCharsets;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -250,7 +251,8 @@ public void testMaybeSampleMaxSize() {
             );
         final ProjectId projectId = projectBuilder.getId();
         ProjectMetadata projectMetadata = projectBuilder.build();
-        final IndexRequest indexRequest = new IndexRequest(indexName).id("_id").source(randomByteArrayOfLength(150), XContentType.JSON);
+        final IndexRequest indexRequest = new IndexRequest(indexName).id("_id")
+            .source(randomAlphanumericOfLength(150).getBytes(StandardCharsets.UTF_8), XContentType.JSON);
         for (int i = 0; i < maxSamples; i++) {
             samplingService.maybeSample(projectMetadata, indexRequest);
         }