diff --git a/seance.js b/seance.js
index 2b51651..6410777 100644
--- a/seance.js
+++ b/seance.js
@@ -340,7 +340,7 @@ class Seance {
 
       // intelligently add ?json attribute
       if (mediumUrl.indexOf('format=json') == -1) {
-        if (mediumUrl.indexOf('?') == 0) {
+        if (mediumUrl.indexOf('?') == -1) {
           mediumUrl = `${mediumUrl}?format=json`
         } else {
           mediumUrl = `${mediumUrl}&format=json`