diff --git a/plugin/src/test/java/org/elasticsearch/xpack/ml/datafeed/ChunkingConfigTests.java b/plugin/src/test/java/org/elasticsearch/xpack/ml/datafeed/ChunkingConfigTests.java
index 505ee27ad7f..9b06ac8de2a 100644
--- a/plugin/src/test/java/org/elasticsearch/xpack/ml/datafeed/ChunkingConfigTests.java
+++ b/plugin/src/test/java/org/elasticsearch/xpack/ml/datafeed/ChunkingConfigTests.java
@@ -54,6 +54,7 @@ public class ChunkingConfigTests extends AbstractSerializingTestCase<ChunkingCon
         ChunkingConfig.Mode mode = randomFrom(ChunkingConfig.Mode.values());
         TimeValue timeSpan = null;
         if (mode == ChunkingConfig.Mode.MANUAL) {
+            // time span is required to be at least 1 millis, so we use a custom method to generate a time value here
             timeSpan = randomPositiveSecondsMinutesHours();
         }
         return new ChunkingConfig(mode, timeSpan);