diff --git a/lib/js/src/thrift.js b/lib/js/src/thrift.js
index 6cab4fd..7a18206 100644
--- a/lib/js/src/thrift.js
+++ b/lib/js/src/thrift.js
@@ -1153,9 +1153,15 @@
      */
     readMapBegin: function() {
         var map = this.rstack.pop();
+        var first = map.shift();
+        if (first instanceof Array) {
+          this.rstack.push(map);
+          map = first;
+          first = map.shift();
+        }
 
         var r = {};
-        r.ktype = Thrift.Protocol.RType[map.shift()];
+        r.ktype = Thrift.Protocol.RType[first];
         r.vtype = Thrift.Protocol.RType[map.shift()];
         r.size = map.shift();