diff --git a/core/src/main/java/org/elasticsearch/index/query/InnerHitBuilder.java b/core/src/main/java/org/elasticsearch/index/query/InnerHitBuilder.java
index 9ef9f2998b0..c1b240066ab 100644
--- a/core/src/main/java/org/elasticsearch/index/query/InnerHitBuilder.java
+++ b/core/src/main/java/org/elasticsearch/index/query/InnerHitBuilder.java
@@ -48,6 +48,7 @@ import java.io.IOException;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
@@ -266,8 +267,10 @@ public final class InnerHitBuilder extends ToXContentToBytes implements Writeabl
         out.writeBoolean(hasScriptFields);
         if (hasScriptFields) {
             out.writeVInt(scriptFields.size());
-            for (ScriptField scriptField : scriptFields) {
-                scriptField.writeTo(out);
+            Iterator<ScriptField> iterator = scriptFields.stream()
+                    .sorted((a, b) -> a.fieldName().compareTo(b.fieldName())).iterator();
+            while (iterator.hasNext()) {
+                iterator.next().writeTo(out);
             }
         }
         out.writeOptionalWriteable(fetchSourceContext);
@@ -285,7 +288,10 @@ public final class InnerHitBuilder extends ToXContentToBytes implements Writeabl
         out.writeBoolean(hasChildInnerHits);
         if (hasChildInnerHits) {
             out.writeVInt(childInnerHits.size());
-            for (Map.Entry<String, InnerHitBuilder> entry : childInnerHits.entrySet()) {
+            Iterator<Map.Entry<String, InnerHitBuilder>> iterator = childInnerHits.entrySet().stream()
+                    .sorted((a, b) -> a.getKey().compareTo(b.getKey())).iterator();
+            while (iterator.hasNext()) {
+                Map.Entry<String, InnerHitBuilder> entry = iterator.next();
                 out.writeString(entry.getKey());
                 entry.getValue().writeTo(out);
             }
diff --git a/core/src/test/java/org/elasticsearch/index/query/InnerHitBuilderTests.java b/core/src/test/java/org/elasticsearch/index/query/InnerHitBuilderTests.java
index 6ebe14620f9..3f480262f49 100644
--- a/core/src/test/java/org/elasticsearch/index/query/InnerHitBuilderTests.java
+++ b/core/src/test/java/org/elasticsearch/index/query/InnerHitBuilderTests.java
@@ -19,6 +19,7 @@
 package org.elasticsearch.index.query;
 
 import org.apache.lucene.search.join.ScoreMode;
+import org.elasticsearch.common.io.stream.BytesStreamOutput;
 import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.xcontent.NamedXContentRegistry;
@@ -36,6 +37,7 @@ import org.elasticsearch.search.fetch.subphase.FetchSourceContext;
 import org.elasticsearch.search.fetch.subphase.InnerHitsContext;
 import org.elasticsearch.search.fetch.subphase.highlight.HighlightBuilderTests;
 import org.elasticsearch.search.internal.SearchContext;
+import org.elasticsearch.search.internal.ShardSearchLocalRequest;
 import org.elasticsearch.search.sort.SortBuilder;
 import org.elasticsearch.search.sort.SortBuilders;
 import org.elasticsearch.search.sort.SortOrder;
@@ -95,6 +97,30 @@ public class InnerHitBuilderTests extends ESTestCase {
         }
     }
 
+    /**
+     * Test that if we serialize and deserialize an object, further
+     * serialization leads to identical bytes representation.
+     *
+     * This is necessary to ensure because we use the serialized BytesReference
+     * of this builder as part of the cacheKey in
+     * {@link ShardSearchLocalRequest} (via
+     * {@link SearchSourceBuilder#collapse(org.elasticsearch.search.collapse.CollapseBuilder)})
+     */
+    public void testSerializationOrder() throws Exception {
+        for (int runs = 0; runs < NUMBER_OF_TESTBUILDERS; runs++) {
+            InnerHitBuilder original = randomInnerHits();
+            InnerHitBuilder deserialized = serializedCopy(original);
+            assertEquals(deserialized, original);
+            assertEquals(deserialized.hashCode(), original.hashCode());
+            assertNotSame(deserialized, original);
+            BytesStreamOutput out1 = new BytesStreamOutput();
+            BytesStreamOutput out2 = new BytesStreamOutput();
+            original.writeTo(out1);
+            deserialized.writeTo(out2);
+            assertEquals(out1.bytes(), out2.bytes());
+        }
+    }
+
     public void testFromAndToXContent() throws Exception {
         for (int runs = 0; runs < NUMBER_OF_TESTBUILDERS; runs++) {
             InnerHitBuilder innerHit = randomInnerHits(true, false);
@@ -114,7 +140,7 @@ public class InnerHitBuilderTests extends ESTestCase {
         }
     }
 
-    public void testEqualsAndHashcode() throws IOException {
+    public void testEqualsAndHashcode() {
         for (int runs = 0; runs < NUMBER_OF_TESTBUILDERS; runs++) {
             checkEqualsAndHashCode(randomInnerHits(), InnerHitBuilderTests::serializedCopy, InnerHitBuilderTests::mutate);
         }