diff --git a/src/vector/app.js b/src/vector/app.js
index c77049f51..6267ed0b9 100644
--- a/src/vector/app.js
+++ b/src/vector/app.js
@@ -54,6 +54,19 @@ import CallHandler from 'matrix-react-sdk/src/CallHandler';
 let lastLocationHashSet = null;
 
 function checkBrowserFeatures(featureList) {
+    // custom checks atop Modernizr because it doesn't have ES2018/ES2019 checks in it for some features we depend on:
+    // ran prior to Modernizr so the missing features are logged even if Modernizr is broken
+    // ES2018: http://www.ecma-international.org/ecma-262/9.0/#sec-promise.prototype.finally
+    if (typeof Promise.prototype.finally !== "function") {
+        console.error("Browser missing feature: Promise.prototype.finally");
+        featureComplete = false;
+    }
+    // ES2019: http://www.ecma-international.org/ecma-262/10.0/#sec-object.fromentries
+    if (typeof Object.fromEntries !== "function") {
+        console.error("Browser missing feature: Object.fromEntries");
+        featureComplete = false;
+    }
+
     if (!window.Modernizr) {
         console.error("Cannot check features - Modernizr global is missing.");
         return false;
@@ -69,11 +82,11 @@ function checkBrowserFeatures(featureList) {
         }
         if (window.Modernizr[featureList[i]] === false) {
             console.error("Browser missing feature: '%s'", featureList[i]);
-            // toggle flag rather than return early so we log all missing features
-            // rather than just the first.
+            // toggle flag rather than return early so we log all missing features rather than just the first.
             featureComplete = false;
         }
     }
+
     return featureComplete;
 }