diff --git a/server/src/main/java/org/elasticsearch/index/mapper/MapperService.java b/server/src/main/java/org/elasticsearch/index/mapper/MapperService.java
index 9cd8ef1f6ac67..15448bb4003d9 100644
--- a/server/src/main/java/org/elasticsearch/index/mapper/MapperService.java
+++ b/server/src/main/java/org/elasticsearch/index/mapper/MapperService.java
@@ -468,11 +468,11 @@ private synchronized Map<String, DocumentMapper> internalMerge(@Nullable Documen
         // commit the change
         if (defaultMappingSource != null) {
             this.defaultMappingSource = defaultMappingSource;
+            this.defaultMapper = defaultMapper;
         }
         if (newMapper != null) {
             this.mapper = newMapper;
         }
-        this.defaultMapper = defaultMapper;
         this.fieldTypes = fieldTypes;
         this.hasNested = hasNested;
         this.fullPathObjectMappers = fullPathObjectMappers;
diff --git a/server/src/test/java/org/elasticsearch/index/mapper/MapperServiceTests.java b/server/src/test/java/org/elasticsearch/index/mapper/MapperServiceTests.java
index 51b6e9d716887..e31cee29e67bf 100644
--- a/server/src/test/java/org/elasticsearch/index/mapper/MapperServiceTests.java
+++ b/server/src/test/java/org/elasticsearch/index/mapper/MapperServiceTests.java
@@ -21,13 +21,16 @@
 
 import org.elasticsearch.ExceptionsHelper;
 import org.elasticsearch.Version;
+import org.elasticsearch.action.admin.indices.mapping.put.PutMappingRequest;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.compress.CompressedXContent;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentFactory;
 import org.elasticsearch.common.xcontent.XContentType;
+import org.elasticsearch.common.xcontent.json.JsonXContent;
 import org.elasticsearch.index.IndexService;
 import org.elasticsearch.index.mapper.KeywordFieldMapper.KeywordFieldType;
 import org.elasticsearch.index.mapper.MapperService.MergeReason;
@@ -119,6 +122,35 @@ public void testIndexIntoDefaultMapping() throws Throwable {
         assertNull(indexService.mapperService().documentMapper(MapperService.DEFAULT_MAPPING));
     }
 
+    public void testIndexMetaDataUpdateDoesNotLoseDefaultMapper() throws IOException {
+        final IndexService indexService =
+                createIndex("test", Settings.builder().put(IndexMetaData.SETTING_VERSION_CREATED, Version.V_6_3_0).build());
+        try (XContentBuilder builder = JsonXContent.contentBuilder()) {
+            builder.startObject();
+            {
+                builder.startObject(MapperService.DEFAULT_MAPPING);
+                {
+                    builder.field("date_detection", false);
+                }
+                builder.endObject();
+            }
+            builder.endObject();
+            final PutMappingRequest putMappingRequest = new PutMappingRequest();
+            putMappingRequest.indices("test");
+            putMappingRequest.type(MapperService.DEFAULT_MAPPING);
+            putMappingRequest.source(builder);
+            client().admin().indices().preparePutMapping("test").setType(MapperService.DEFAULT_MAPPING).setSource(builder).get();
+        }
+        assertNotNull(indexService.mapperService().documentMapper(MapperService.DEFAULT_MAPPING));
+        final Settings zeroReplicasSettings = Settings.builder().put(IndexMetaData.SETTING_NUMBER_OF_REPLICAS, 0).build();
+        client().admin().indices().prepareUpdateSettings("test").setSettings(zeroReplicasSettings).get();
+        /*
+         * This assertion is a guard against a previous bug that would lose the default mapper when applying a metadata update that did not
+         * update the default mapping.
+         */
+        assertNotNull(indexService.mapperService().documentMapper(MapperService.DEFAULT_MAPPING));
+    }
+
     public void testTotalFieldsExceedsLimit() throws Throwable {
         Function<String, String> mapping = type -> {
             try {