diff --git a/src/main/java/org/elasticsearch/search/fetch/source/FetchSourceSubPhase.java b/src/main/java/org/elasticsearch/search/fetch/source/FetchSourceSubPhase.java
index d4d208aab4afb..76106861c80cc 100644
--- a/src/main/java/org/elasticsearch/search/fetch/source/FetchSourceSubPhase.java
+++ b/src/main/java/org/elasticsearch/search/fetch/source/FetchSourceSubPhase.java
@@ -22,12 +22,14 @@
 import com.google.common.collect.ImmutableMap;
 import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.common.inject.Inject;
+import org.elasticsearch.common.io.stream.BytesStreamOutput;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentFactory;
 import org.elasticsearch.search.SearchParseElement;
 import org.elasticsearch.search.fetch.FetchSubPhase;
 import org.elasticsearch.search.internal.InternalSearchHit;
 import org.elasticsearch.search.internal.SearchContext;
+import org.elasticsearch.search.lookup.SourceLookup;
 
 import java.io.IOException;
 import java.util.Map;
@@ -71,9 +73,12 @@ public void hitExecute(SearchContext context, HitContext hitContext) throws Elas
             return;
         }
 
-        Object value = context.lookup().source().filter(fetchSourceContext.includes(), fetchSourceContext.excludes());
+        SourceLookup source = context.lookup().source();
+        Object value = source.filter(fetchSourceContext.includes(), fetchSourceContext.excludes());
         try {
-            XContentBuilder builder = XContentFactory.contentBuilder(context.lookup().source().sourceContentType());
+            final int initialCapacity = Math.min(1024, source.internalSourceRef().length());
+            BytesStreamOutput streamOutput = new BytesStreamOutput(initialCapacity);
+            XContentBuilder builder = new XContentBuilder(context.lookup().source().sourceContentType().xContent(), streamOutput);
             builder.value(value);
             hitContext.hit().sourceRef(builder.bytes());
         } catch (IOException e) {