diff --git a/elasticsearch/serializer.py b/elasticsearch/serializer.py
index 970db113..1e932c3d 100644
--- a/elasticsearch/serializer.py
+++ b/elasticsearch/serializer.py
@@ -21,7 +21,11 @@ class JSONSerializer(object):
     def dumps(self, data):
         # don't serialize strings
         if isinstance(data, (type(''), type(u''))):
-            return data
+            try:
+                return data.encode('utf-8')
+            except UnicodeDecodeError:
+                # Python 2 and str, no need to re-encode
+                return data
 
         try:
             return json.dumps(data, default=self.default)