diff --git a/src/core/components/parameter-row.jsx b/src/core/components/parameter-row.jsx
index a436c527..909170dd 100644
--- a/src/core/components/parameter-row.jsx
+++ b/src/core/components/parameter-row.jsx
@@ -116,7 +116,7 @@ export default class ParameterRow extends Component {
             { isOAS3 && isOAS3() && param.get("deprecated") ? "deprecated": null }
           </div>
           <div className="parameter__in">({ param.get("in") })</div>
-          { !extensions.length ? null : extensions.map((v, key) => <ParameterExt key={`${key}-${v}`} xKey={key} xVal={v} /> )}
+          { !extensions.size ? null : extensions.map((v, key) => <ParameterExt key={`${key}-${v}`} xKey={key} xVal={v} /> )}
         </td>
 
         <td className="col parameters-col_description">