diff --git a/plugin/src/main/java/org/elasticsearch/xpack/ml/job/results/ModelPlot.java b/plugin/src/main/java/org/elasticsearch/xpack/ml/job/results/ModelPlot.java
index 1a34194de7b..7027c550717 100644
--- a/plugin/src/main/java/org/elasticsearch/xpack/ml/job/results/ModelPlot.java
+++ b/plugin/src/main/java/org/elasticsearch/xpack/ml/job/results/ModelPlot.java
@@ -87,7 +87,10 @@ public class ModelPlot implements ToXContentObject, Writeable {
     private double modelLower;
     private double modelUpper;
     private double modelMedian;
-    private double actual;
+    /**
+     * This can be <code>null</code> because buckets where no values were observed will still have a model, but no actual
+     */
+    private Double actual;
 
     public ModelPlot(String jobId, Date timestamp, long bucketSpan) {
         this.jobId = jobId;
@@ -121,7 +124,11 @@ public class ModelPlot implements ToXContentObject, Writeable {
         modelLower = in.readDouble();
         modelUpper = in.readDouble();
         modelMedian = in.readDouble();
-        actual = in.readDouble();
+        if (in.getVersion().before(Version.V_6_0_0_rc1)) {
+            actual = in.readDouble();
+        } else {
+            actual = in.readOptionalDouble();
+        }
         if (in.getVersion().onOrAfter(Version.V_5_5_0)) {
             bucketSpan = in.readLong();
         } else {
@@ -156,7 +163,17 @@ public class ModelPlot implements ToXContentObject, Writeable {
         out.writeDouble(modelLower);
         out.writeDouble(modelUpper);
         out.writeDouble(modelMedian);
-        out.writeDouble(actual);
+        if (out.getVersion().before(Version.V_6_0_0_rc1)) {
+            if (actual == null) {
+                // older versions cannot accommodate null, so we have no choice but to propagate the bug of
+                // https://github.com/elastic/x-pack-elasticsearch/issues/2528
+                out.writeDouble(0.0);
+            } else {
+                out.writeDouble(actual);
+            }
+        } else {
+            out.writeOptionalDouble(actual);
+        }
         if (out.getVersion().onOrAfter(Version.V_5_5_0)) {
             out.writeLong(bucketSpan);
         }
@@ -196,7 +213,9 @@ public class ModelPlot implements ToXContentObject, Writeable {
         builder.field(MODEL_LOWER.getPreferredName(), modelLower);
         builder.field(MODEL_UPPER.getPreferredName(), modelUpper);
         builder.field(MODEL_MEDIAN.getPreferredName(), modelMedian);
-        builder.field(ACTUAL.getPreferredName(), actual);
+        if (actual != null) {
+            builder.field(ACTUAL.getPreferredName(), actual);
+        }
         builder.endObject();
         return builder;
     }
@@ -302,11 +321,11 @@ public class ModelPlot implements ToXContentObject, Writeable {
         this.modelMedian = modelMedian;
     }
 
-    public double getActual() {
+    public Double getActual() {
         return actual;
     }
 
-    public void setActual(double actual) {
+    public void setActual(Double actual) {
         this.actual = actual;
     }
 
@@ -331,7 +350,7 @@ public class ModelPlot implements ToXContentObject, Writeable {
                 this.modelLower == that.modelLower &&
                 this.modelUpper == that.modelUpper &&
                 this.modelMedian == that.modelMedian &&
-                this.actual == that.actual &&
+                Objects.equals(this.actual, that.actual) &&
                 this.bucketSpan ==  that.bucketSpan;
     }
 
diff --git a/plugin/src/test/java/org/elasticsearch/xpack/ml/job/results/ModelPlotTests.java b/plugin/src/test/java/org/elasticsearch/xpack/ml/job/results/ModelPlotTests.java
index 0354a5933e4..c6e316ed11f 100644
--- a/plugin/src/test/java/org/elasticsearch/xpack/ml/job/results/ModelPlotTests.java
+++ b/plugin/src/test/java/org/elasticsearch/xpack/ml/job/results/ModelPlotTests.java
@@ -6,12 +6,19 @@
 package org.elasticsearch.xpack.ml.job.results;
 
 import org.elasticsearch.common.io.stream.Writeable.Reader;
+import org.elasticsearch.common.xcontent.ToXContent;
+import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentParser;
+import org.elasticsearch.common.xcontent.json.JsonXContent;
 import org.elasticsearch.test.AbstractSerializingTestCase;
 
+import java.io.IOException;
 import java.util.Date;
 import java.util.Objects;
 
+import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.not;
+
 public class ModelPlotTests extends AbstractSerializingTestCase<ModelPlot> {
 
     @Override
@@ -172,6 +179,15 @@ public class ModelPlotTests extends AbstractSerializingTestCase<ModelPlot> {
         assertFalse(modelPlot2.equals(modelPlot1));
     }
 
+    public void testEquals_GivenDifferentOneNullActual() {
+        ModelPlot modelPlot1 = createFullyPopulated();
+        ModelPlot modelPlot2 = createFullyPopulated();
+        modelPlot2.setActual(null);
+
+        assertFalse(modelPlot1.equals(modelPlot2));
+        assertFalse(modelPlot2.equals(modelPlot1));
+    }
+
     public void testEquals_GivenEqualmodelPlots() {
         ModelPlot modelPlot1 = createFullyPopulated();
         ModelPlot modelPlot2 = createFullyPopulated();
@@ -181,6 +197,17 @@ public class ModelPlotTests extends AbstractSerializingTestCase<ModelPlot> {
         assertEquals(modelPlot1.hashCode(), modelPlot2.hashCode());
     }
 
+    public void testToXContent_GivenNullActual() throws IOException {
+        XContentBuilder builder = JsonXContent.contentBuilder();
+
+        ModelPlot modelPlot = createFullyPopulated();
+        modelPlot.setActual(null);
+        modelPlot.toXContent(builder, ToXContent.EMPTY_PARAMS);
+
+        String json = builder.string();
+        assertThat(json, not(containsString("actual")));
+    }
+
     public void testId() {
         ModelPlot plot = new ModelPlot("job-foo", new Date(100L), 60L);