diff --git a/core/src/main/java/org/elasticsearch/search/fetch/subphase/ParentFieldSubFetchPhase.java b/core/src/main/java/org/elasticsearch/search/fetch/subphase/ParentFieldSubFetchPhase.java
index ccfbf3515fc..cb8310975fc 100644
--- a/core/src/main/java/org/elasticsearch/search/fetch/subphase/ParentFieldSubFetchPhase.java
+++ b/core/src/main/java/org/elasticsearch/search/fetch/subphase/ParentFieldSubFetchPhase.java
@@ -47,6 +47,11 @@ public final class ParentFieldSubFetchPhase implements FetchSubPhase {
         }
 
         String parentId = getParentId(parentFieldMapper, hitContext.reader(), hitContext.docId());
+        if (parentId == null) {
+            // hit has no _parent field. Can happen for nested inner hits if parent hit is a p/c document.
+            return;
+        }
+
         Map<String, SearchHitField> fields = hitContext.hit().fieldsOrNull();
         if (fields == null) {
             fields = new HashMap<>();
@@ -59,8 +64,7 @@ public final class ParentFieldSubFetchPhase implements FetchSubPhase {
         try {
             SortedDocValues docValues = reader.getSortedDocValues(fieldMapper.name());
             BytesRef parentId = docValues.get(docId);
-            assert parentId.length > 0;
-            return parentId.utf8ToString();
+            return parentId.length > 0 ? parentId.utf8ToString() : null;
         } catch (IOException e) {
             throw ExceptionsHelper.convertToElastic(e);
         }
diff --git a/core/src/test/java/org/elasticsearch/search/fetch/subphase/InnerHitsIT.java b/core/src/test/java/org/elasticsearch/search/fetch/subphase/InnerHitsIT.java
index 86ca66eb87c..809591cd688 100644
--- a/core/src/test/java/org/elasticsearch/search/fetch/subphase/InnerHitsIT.java
+++ b/core/src/test/java/org/elasticsearch/search/fetch/subphase/InnerHitsIT.java
@@ -995,4 +995,21 @@ public class InnerHitsIT extends ESIntegTestCase {
                 equalTo("fox ate rabbit x y z"));
     }
 
+    public void testNestedInnerHitWrappedInParentChildInnerhit() throws Exception {
+        assertAcked(prepareCreate("test").addMapping("child_type", "_parent", "type=parent_type", "nested_type", "type=nested"));
+        client().prepareIndex("test", "parent_type", "1").setSource("key", "value").get();
+        client().prepareIndex("test", "child_type", "2").setParent("1").setSource("nested_type", Collections.singletonMap("key", "value"))
+            .get();
+        refresh();
+        SearchResponse response = client().prepareSearch("test")
+            .setQuery(boolQuery().must(matchQuery("key", "value"))
+                .should(hasChildQuery("child_type", nestedQuery("nested_type", matchAllQuery(), ScoreMode.None)
+                    .innerHit(new InnerHitBuilder()), ScoreMode.None).innerHit(new InnerHitBuilder())))
+            .get();
+        assertHitCount(response, 1);
+        SearchHit hit = response.getHits().getAt(0);
+        assertThat(hit.getInnerHits().get("child_type").getAt(0).field("_parent").getValue(), equalTo("1"));
+        assertThat(hit.getInnerHits().get("child_type").getAt(0).getInnerHits().get("nested_type").getAt(0).field("_parent"), nullValue());
+    }
+
 }