diff --git a/lib/protocol.js b/lib/protocol.js
index 3d7756d..0d0cece 100644
--- a/lib/protocol.js
+++ b/lib/protocol.js
@@ -1180,7 +1180,7 @@ function sizeOfArray(value, typeArgs, rootNode) {
 function getField(countField, rootNode) {
     var countFieldArr = countField.split(".");
     var count = rootNode;
-    for (var index in countFieldArr) {
+    for (var index = 0; index < countFieldArr.length; index++) {
         count = count[countFieldArr[index]];
     }
     return count;