diff --git a/server/src/main/java/org/elasticsearch/cluster/metadata/MetadataCreateIndexService.java b/server/src/main/java/org/elasticsearch/cluster/metadata/MetadataCreateIndexService.java
index 5b1df19dfaaed..4453e8167fa11 100644
--- a/server/src/main/java/org/elasticsearch/cluster/metadata/MetadataCreateIndexService.java
+++ b/server/src/main/java/org/elasticsearch/cluster/metadata/MetadataCreateIndexService.java
@@ -591,8 +591,7 @@ static Map<String, Map<String, Object>> parseV2Mappings(String mappingsJson, Lis
                 Map<String, Object> innerTemplateNonProperties = new HashMap<>(innerTemplateMapping);
                 Map<String, Object> maybeProperties = (Map<String, Object>) innerTemplateNonProperties.remove("properties");
 
-                XContentHelper.mergeDefaults(innerTemplateNonProperties, nonProperties);
-                nonProperties = innerTemplateNonProperties;
+                nonProperties = mergeFailingOnReplacement(nonProperties, innerTemplateNonProperties);
 
                 if (maybeProperties != null) {
                     properties = mergeFailingOnReplacement(properties, maybeProperties);
@@ -605,8 +604,7 @@ static Map<String, Map<String, Object>> parseV2Mappings(String mappingsJson, Lis
             Map<String, Object> innerRequestNonProperties = new HashMap<>(innerRequestMappings);
             Map<String, Object> maybeRequestProperties = (Map<String, Object>) innerRequestNonProperties.remove("properties");
 
-            XContentHelper.mergeDefaults(innerRequestNonProperties, nonProperties);
-            nonProperties = innerRequestNonProperties;
+            nonProperties = mergeFailingOnReplacement(nonProperties, innerRequestNonProperties);
 
             if (maybeRequestProperties != null) {
                 properties = mergeFailingOnReplacement(properties, maybeRequestProperties);
diff --git a/server/src/main/java/org/elasticsearch/cluster/metadata/MetadataIndexTemplateService.java b/server/src/main/java/org/elasticsearch/cluster/metadata/MetadataIndexTemplateService.java
index 5c4d5db655d34..6efa323e5947f 100644
--- a/server/src/main/java/org/elasticsearch/cluster/metadata/MetadataIndexTemplateService.java
+++ b/server/src/main/java/org/elasticsearch/cluster/metadata/MetadataIndexTemplateService.java
@@ -987,14 +987,12 @@ private static void validateCompositeTemplate(final ClusterState state,
 
                 // Parse mappings to ensure they are valid after being composed
                 List<CompressedXContent> mappings = resolveMappings(stateWithIndex, templateName);
-                final Map<String, Map<String, Object>> finalMappings;
                 try {
+                    Map<String, Map<String, Object>> finalMappings =
+                        MetadataCreateIndexService.parseV2Mappings("{}", mappings, xContentRegistry);
                     MapperService dummyMapperService = tempIndexService.mapperService();
-                    for (CompressedXContent mapping : mappings) {
-                        // TODO: Eventually change this to:
-                        // dummyMapperService.merge(MapperService.SINGLE_MAPPING_NAME, mapping, MergeReason.INDEX_TEMPLATE);
-                        dummyMapperService.merge(MapperService.SINGLE_MAPPING_NAME, mapping, MergeReason.MAPPING_UPDATE);
-                    }
+                        // TODO: Eventually change this to use MergeReason.INDEX_TEMPLATE
+                        dummyMapperService.merge(finalMappings, MergeReason.MAPPING_UPDATE);
                 } catch (Exception e) {
                     throw new IllegalArgumentException("invalid composite mappings for [" + templateName + "]", e);
                 }