diff --git a/blocks/procedures.js b/blocks/procedures.js
index a1db16baa..3019b0b9c 100644
--- a/blocks/procedures.js
+++ b/blocks/procedures.js
@@ -131,7 +131,7 @@ Blockly.Blocks['procedures_defnoreturn'] = {
       var parameter = document.createElement('arg');
       var argModel = this.argumentVarModels_[i];
       parameter.setAttribute('name', argModel.name);
-      parameter.setAttribute('var-id', argModel.getId());
+      parameter.setAttribute('varid', argModel.getId());
       if (opt_paramIds && this.paramIds_) {
         parameter.setAttribute('paramId', this.paramIds_[i]);
       }
@@ -155,7 +155,7 @@ Blockly.Blocks['procedures_defnoreturn'] = {
     for (var i = 0, childNode; childNode = xmlElement.childNodes[i]; i++) {
       if (childNode.nodeName.toLowerCase() == 'arg') {
         var varName = childNode.getAttribute('name');
-        var varId = childNode.getAttribute('var-id') || childNode.getAttribute('varId');
+        var varId = childNode.getAttribute('varid') || childNode.getAttribute('varId');
         this.arguments_.push(varName);
         var variable = Blockly.Variables.getOrCreateVariablePackage(
             this.workspace, varId, varName, '');