diff --git a/server/src/main/java/org/elasticsearch/action/admin/indices/shrink/ResizeRequest.java b/server/src/main/java/org/elasticsearch/action/admin/indices/shrink/ResizeRequest.java
index 2b6de1bb47900..46e3a5fdc3e60 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/indices/shrink/ResizeRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/indices/shrink/ResizeRequest.java
@@ -226,6 +226,9 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
                 }
             }
             builder.endObject();
+            if (maxSinglePrimarySize != null) {
+                builder.field(MAX_SINGLE_PRIMARY_SIZE.getPreferredName(), maxSinglePrimarySize);
+            }
         }
         builder.endObject();
         return builder;
diff --git a/server/src/test/java/org/elasticsearch/action/admin/indices/shrink/ResizeRequestTests.java b/server/src/test/java/org/elasticsearch/action/admin/indices/shrink/ResizeRequestTests.java
index c3bf3ed9aa9f2..99218d1545083 100644
--- a/server/src/test/java/org/elasticsearch/action/admin/indices/shrink/ResizeRequestTests.java
+++ b/server/src/test/java/org/elasticsearch/action/admin/indices/shrink/ResizeRequestTests.java
@@ -14,6 +14,8 @@
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.unit.ByteSizeUnit;
+import org.elasticsearch.common.unit.ByteSizeValue;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.common.xcontent.XContentType;
 import org.elasticsearch.index.RandomCreateIndexGenerator;
@@ -55,6 +57,12 @@ public void testToXContent() throws IOException {
             String actualRequestBody = Strings.toString(request);
             assertEquals("{\"settings\":{},\"aliases\":{}}", actualRequestBody);
         }
+        {
+            ResizeRequest request = new ResizeRequest("target", "source");
+            request.setMaxSinglePrimarySize(new ByteSizeValue(100, ByteSizeUnit.MB));
+            String actualRequestBody = Strings.toString(request);
+            assertEquals("{\"settings\":{},\"aliases\":{},\"max_single_primary_size\":\"100mb\"}", actualRequestBody);
+        }
         {
             ResizeRequest request = new ResizeRequest();
             CreateIndexRequest target = new CreateIndexRequest("target");