diff --git a/lib/js/thrift.js b/lib/js/thrift.js
index c7a46fd..f4e7235 100644
--- a/lib/js/thrift.js
+++ b/lib/js/thrift.js
@@ -460,7 +460,8 @@
                 map = ',' + map;
             }
 
-            map = '"' + k + '":' + v + map;
+            if ( ! isNaN(k)) { k = '"' + k + '"'; } //json "keys" need to be strings
+            map = k + ':' + v + map;
         }
         map = '{' + map;