diff --git a/lib/extensions.js b/lib/extensions.js
index 999deeb9..d431c3ab 100644
--- a/lib/extensions.js
+++ b/lib/extensions.js
@@ -44,7 +44,7 @@ module.exports = function(realmConstructor) {
     Object.defineProperties(realmConstructor, getOwnPropertyDescriptors({
         open(config) {
             return new Promise((resolve, reject) => {
-                const realm = new Realm(config);
+                const realm = new realmConstructor(config);
                 realm.wait((error) => {
                     if (error) {
                         reject(new Error("Cannot asynchronously open synced Realm, because the associated session previously experienced a fatal error"));
@@ -56,7 +56,7 @@ module.exports = function(realmConstructor) {
         },
 
         openAsync(config, callback) {
-            const realm = new Realm(config);
+            const realm = new realmConstructor(config);
             realm.wait((error) => {
                 if (error) {
                     callback(new Error("Cannot asynchronously open synced Realm, because the associated session previously experienced a fatal error"));