diff --git a/solr/CHANGES.txt b/solr/CHANGES.txt
index 5012c64c4ad..070aa0959c1 100644
--- a/solr/CHANGES.txt
+++ b/solr/CHANGES.txt
@@ -93,6 +93,9 @@ Improvements
 * SOLR-13720: BlockJoinParentQParser.getCachedFilter()made public for accessing from QParser plugins
   (Stanislav Livotov via Mikhail Khludnev)
 
+* SOLR-13728: If a partial update (aka atomic update) is attempted on a document that has child docs, then ensure
+  the schema supports it (_root_ stored/docValues) by throwing an exception. (David Smiley)
+
 Bug Fixes
 ----------------------
 
diff --git a/solr/core/src/java/org/apache/solr/schema/IndexSchema.java b/solr/core/src/java/org/apache/solr/schema/IndexSchema.java
index da2b71acfb2..980be8d6007 100644
--- a/solr/core/src/java/org/apache/solr/schema/IndexSchema.java
+++ b/solr/core/src/java/org/apache/solr/schema/IndexSchema.java
@@ -1974,6 +1974,17 @@ public class IndexSchema {
     return nestPathType instanceof NestPathField;
   }
 
+  /**
+   * Does this schema supports partial updates (aka atomic updates) and child docs as well.
+   */
+  public boolean supportsPartialUpdatesOfChildDocs() {
+    if (savesChildDocRelations() == false) {
+      return false;
+    }
+    SchemaField rootField = getField(IndexSchema.ROOT_FIELD_NAME);
+    return rootField.stored() || rootField.hasDocValues();
+  }
+
   public PayloadDecoder getPayloadDecoder(String field) {
     FieldType ft = getFieldType(field);
     if (ft == null)
diff --git a/solr/core/src/java/org/apache/solr/update/processor/DistributedUpdateProcessor.java b/solr/core/src/java/org/apache/solr/update/processor/DistributedUpdateProcessor.java
index 11667c8a60c..5e04077fb39 100644
--- a/solr/core/src/java/org/apache/solr/update/processor/DistributedUpdateProcessor.java
+++ b/solr/core/src/java/org/apache/solr/update/processor/DistributedUpdateProcessor.java
@@ -23,6 +23,8 @@ import java.util.Set;
 import java.util.concurrent.TimeUnit;
 
 import com.google.common.annotations.VisibleForTesting;
+import org.apache.lucene.index.Term;
+import org.apache.lucene.search.TermQuery;
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.CharsRefBuilder;
 import org.apache.solr.client.solrj.SolrRequest;
@@ -693,6 +695,13 @@ public class DistributedUpdateProcessor extends UpdateRequestProcessor {
       // create a new doc by default if an old one wasn't found
       mergedDoc = docMerger.merge(sdoc, new SolrInputDocument());
     } else {
+      // Safety check: don't allow an update to an existing doc that has children, unless we actually support this.
+      if (req.getSchema().isUsableForChildDocs() // however, next line we see it doesn't support child docs
+          && req.getSchema().supportsPartialUpdatesOfChildDocs() == false
+          && req.getSearcher().count(new TermQuery(new Term(IndexSchema.ROOT_FIELD_NAME, idBytes))) > 1) {
+        throw new SolrException(ErrorCode.BAD_REQUEST, "This schema does not support partial updates to nested docs. See ref guide.");
+      }
+
       String oldRootDocRootFieldVal = (String) oldRootDocWithChildren.getFieldValue(IndexSchema.ROOT_FIELD_NAME);
       if(req.getSchema().savesChildDocRelations() && oldRootDocRootFieldVal != null &&
           !idString.equals(oldRootDocRootFieldVal)) {
diff --git a/solr/core/src/test/org/apache/solr/update/processor/AtomicUpdatesTest.java b/solr/core/src/test/org/apache/solr/update/processor/AtomicUpdatesTest.java
index 6c66285160c..12404862887 100644
--- a/solr/core/src/test/org/apache/solr/update/processor/AtomicUpdatesTest.java
+++ b/solr/core/src/test/org/apache/solr/update/processor/AtomicUpdatesTest.java
@@ -18,6 +18,7 @@ package org.apache.solr.update.processor;
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.Date;
 import java.util.List;
 
@@ -1179,6 +1180,36 @@ public class AtomicUpdatesTest extends SolrTestCaseJ4 {
         "/response/docs/[0]/single_i_dvn==5");
   }
 
+  /**
+   * Test what happens if we try to update the parent of a doc with children.
+   * This fails because _root_ is not stored which is currently required for doing this.
+   */
+  @Test
+  public void testUpdateNestedDocUnsupported() throws Exception {
+    assertU(adoc(sdoc(
+        "id", "1",
+        "children", Arrays.asList(sdoc(
+            "id", "100",
+            "cat", "childCat1")
+        )
+    )));
+
+    assertU(commit());
+
+    // update the parent doc to have a category
+    try {
+      assertU(adoc(sdoc(
+          "id", "1",
+          "cat", Collections.singletonMap("add", Arrays.asList("parentCat"))
+      )));
+      fail("expected a failure");
+    } catch (Exception e) {
+      assertEquals("org.apache.solr.common.SolrException: " +
+          "This schema does not support partial updates to nested docs. See ref guide.", e.toString());
+    }
+
+  }
+
   @Test
   public void testInvalidOperation() {
     SolrInputDocument doc;