diff --git a/db/mongodb/src/com/yahoo/ycsb/db/MongoDbClient.java b/db/mongodb/src/com/yahoo/ycsb/db/MongoDbClient.java
index 5146af4f20428d16bf43da555a400c3ce23b15df..df70e148f7ba34b106ce009c6e3fcfa79ca975cf 100644
--- a/db/mongodb/src/com/yahoo/ycsb/db/MongoDbClient.java
+++ b/db/mongodb/src/com/yahoo/ycsb/db/MongoDbClient.java
@@ -148,8 +148,9 @@ public class MongoDbClient extends DB {
 
             DBCollection collection = db.getCollection(table);
             DBObject r = new BasicDBObject().append("_id", key);
-            r.putAll(values);
-
+	    for(String k: values.keySet()) {
+		r.put(k, values.get(k).toString());
+	    }
             collection.setWriteConcern(writeConcern);
 
             collection.insert(r);