diff --git a/plugin/src/main/java/org/elasticsearch/xpack/ml/action/UpdateProcessAction.java b/plugin/src/main/java/org/elasticsearch/xpack/ml/action/UpdateProcessAction.java
index 7c480f10799..508d5193188 100644
--- a/plugin/src/main/java/org/elasticsearch/xpack/ml/action/UpdateProcessAction.java
+++ b/plugin/src/main/java/org/elasticsearch/xpack/ml/action/UpdateProcessAction.java
@@ -142,7 +142,7 @@ public class UpdateProcessAction extends
             super.readFrom(in);
             modelPlotConfig = in.readOptionalWriteable(ModelPlotConfig::new);
             if (in.readBoolean()) {
-                in.readList(JobUpdate.DetectorUpdate::new);
+                detectorUpdates = in.readList(JobUpdate.DetectorUpdate::new);
             }
         }
 
diff --git a/plugin/src/test/java/org/elasticsearch/xpack/ml/action/UpdateProcessActionRequestTests.java b/plugin/src/test/java/org/elasticsearch/xpack/ml/action/UpdateProcessActionRequestTests.java
index 984485a317f..60ddb1495d4 100644
--- a/plugin/src/test/java/org/elasticsearch/xpack/ml/action/UpdateProcessActionRequestTests.java
+++ b/plugin/src/test/java/org/elasticsearch/xpack/ml/action/UpdateProcessActionRequestTests.java
@@ -9,6 +9,7 @@ import org.elasticsearch.test.AbstractStreamableTestCase;
 import org.elasticsearch.xpack.ml.job.config.JobUpdate;
 import org.elasticsearch.xpack.ml.job.config.ModelPlotConfig;
 
+import java.util.ArrayList;
 import java.util.List;
 
 public class UpdateProcessActionRequestTests extends AbstractStreamableTestCase<UpdateProcessAction.Request> {
@@ -22,9 +23,10 @@ public class UpdateProcessActionRequestTests extends AbstractStreamableTestCase<
         }
         List<JobUpdate.DetectorUpdate> updates = null;
         if (randomBoolean()) {
+            updates = new ArrayList<>();
             int detectorUpdateCount = randomIntBetween(0, 5);
             for (int i = 0; i < detectorUpdateCount; i++) {
-                new JobUpdate.DetectorUpdate(randomInt(), randomAlphaOfLength(10), null);
+                updates.add(new JobUpdate.DetectorUpdate(randomInt(), randomAlphaOfLength(10), null));
             }
         }
         return new UpdateProcessAction.Request(randomAlphaOfLength(10), config, updates);