diff --git a/javascript/src/utilities/emailUtilities.js b/javascript/src/utilities/emailUtilities.js
index b1aae2570cf8bd0f2da72dd1b6e2d1645b3365b9..d9131fb2f095912e1ee65552d3bcaa756ea7b674 100644
--- a/javascript/src/utilities/emailUtilities.js
+++ b/javascript/src/utilities/emailUtilities.js
@@ -142,7 +142,7 @@ export const prepareVCardParts = parts => {
   }
   for (const part of parts) {
     if (part.body) {
-      if (part.body instanceof String) {
+      if (typeof part.body === "string") {
         part.body = stringToUtf8Base64(part.body);
       } else
       if (part.body instanceof Uint8Array) {